Water-based pressure-sensitive adhesive compositions

ABSTRACT

A pressure-sensitive adhesive is provided that is a dried product of a latex composition, which is formed from an emulsion composition. The latex composition and the emulsion composition are also provided. The emulsion composition has droplets that contain various monomers plus a (meth)acrylate polymer dissolved in the monomers. Additionally, an article containing a layer of the pressure-sensitive adhesive and a method of forming the pressure-sensitive adhesive are provided. The pressure-sensitive adhesives often have both high peel adhesion and high shear strength (i.e., high cohesive strength or high shear holding power).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 ofPCT/US2015/065534, filed Dec. 14, 2015, which claims the benefit of U.S.Provisional Application No. 62/097,784, filed Dec. 30, 2014, thedisclosure of which is incorporated by reference in its/their entiretyherein.

TECHNICAL FIELD

A pressure-sensitive adhesive, a latex composition used to form thepressure-sensitive adhesive, and an emulsion composition used to formthe latex composition are provided.

BACKGROUND

Pressure-sensitive adhesive (PSA) tapes are virtually ubiquitous in thehome and workplace. In one of its simplest configurations, apressure-sensitive tape includes a backing layer and an adhesive layerattached to the backing layer. According to the Pressure-Sensitive TapeCouncil, pressure-sensitive adhesives are known to possess propertiesincluding the following: (1) aggressive and permanent tack, (2)adherence with no more than finger pressure, (3) sufficient ability tohold onto an adherend, and (4) sufficient cohesive strength to beremoved cleanly from the adherend. Materials that have been found tofunction well as PSAs include polymers designed and formulated toexhibit the requisite viscoelastic properties resulting in a desiredbalance of tack, peel adhesion, and shear holding power. PSAs arecharacterized by being normally tacky at room temperature (e.g., about20° C. to 25° C.). Materials that are merely sticky or that adhere to asurface do not necessarily constitute a PSA; the term PSA encompassesmaterials with additional viscoelastic properties.

Acrylic-based pressure-sensitive adhesives have been widely used. Thesepressure-sensitive adhesive compositions can be prepared with or withoutan organic solvent. PSA compositions containing organic solvents, whilecurrently dominant in the marketplace, are decreasing in importance dueto various issues such as pollution, high energy consumption, andflammability associated with the use of organic solvents. That is, theadhesive industry is increasingly focused on adhesive compositions thathave either low or no organic solvent content.

Some such adhesive compositions can, for example, be prepared fromwater-based latex compositions formed by emulsion polymerization. Suchadhesives are described, for example, in U.S. Pat. No. 5,686,518(Fontenot et al.), U.S. Pat. No. 6,710,128 (Helmer et al.), U.S. Pat.No. 6,511,744 (Centner et al.), U.S. Pat. No. 6,048,611 (Lu et al.),U.S. Pat. No. 4,912,169 (Whitmire et al.), U.S. Pat. No. 6,657,011 (Lauet al.), U.S. Pat. No. 8,258,240 (Suzuki et al.), and U.S. PatentApplication Publication No. 2010/0081764 (Ouzineb et al.).

SUMMARY

A pressure-sensitive adhesive is provided that is the dried product of alatex composition, which is formed from an emulsion composition. Thelatex composition and the emulsion composition are also provided.Additionally, an article containing the pressure-sensitive adhesive anda method of forming the pressure-sensitive adhesive are provided. Thepressure-sensitive adhesive has a good balance of peel adhesion andshear strength (i.e., cohesion) at both room temperature (e.g., about20° C. to about 25° C.) and elevated temperatures (e.g., around about70° C.), particularly when adhered to low surface energy substrates.

In a first aspect, an emulsion composition is provided that contains a)water, b) a polymerizable surfactant having an unsaturated group thatcan undergo free radical polymerization, c) a first monomer composition,and d) a second (meth)acrylate polymer. The first monomer compositionincludes an alkyl (meth)acrylate having a linear or branched alkyl groupwith at least six carbon atoms. The second (meth)acrylate polymer ispresent in an amount of 0.5 to 15 weight percent based on a total weightof monomers in the first monomer composition and has a glass transitiontemperature greater than or equal to 50° C. The second (meth)acrylatepolymer is formed from a second monomer composition containing at least50 weight percent of a cyclic alkyl (meth)acrylate based on a totalweight of monomers in the second monomer composition, wherein the cyclicalkyl group has at least six carbon atoms. The emulsion compositioncontains a first phase that includes the water and a second phasedispersed as droplets within the first phase. The droplets contain amixture of i) at least 90 weight percent of the first monomercomposition and ii) the second (meth)acrylate polymer. The second(meth)acrylate polymer is not miscible with the first phase and isdissolved in the first monomer composition within the droplets.

In a second aspect, a latex composition is provided that contains areaction product (i.e., polymerized product) of an emulsion composition,wherein the latex composition contains polymeric latex particles. Theemulsion composition is the same as described above.

In a third aspect, a pressure-sensitive adhesive is provided that is adried product of a latex composition. The latex composition contains areaction product (i.e., polymerized product) of an emulsion composition,wherein the latex composition contains polymeric latex particles. Theemulsion composition is the same as described above.

In a fourth aspect, an article is provided. The article contains asubstrate and a first pressure-sensitive adhesive layer positionedadjacent to (and adhered to directly or indirectly) a first majorsurface of the substrate. The pressure-sensitive adhesive layer is adried product of a latex composition. The latex composition contains areaction product (i.e., polymerized product) of an emulsion composition,wherein the latex composition contains polymeric latex particles. Theemulsion composition is the same as described above.

In a fifth aspect, a method of forming a pressure-sensitive adhesive isprovided. The method includes a) forming an emulsion composition asdescribed above; b) polymerizing the emulsion composition to form alatex composition comprising polymeric latex particles; and c) dryingthe latex composition to form the pressure-sensitive adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the Modulated Differential Scanning Calorimetry plot from thesecond heating (2H) cycle for the polymeric latex particles ofExample 1. Heat flow is plotted as a function of temperature in anitrogen atmosphere.

FIG. 2 is the Modulated Differential Scanning Calorimetry plot from thesecond heating (2H) cycle for the polymeric latex particles of Example2. Heat flow is plotted as a function of temperature in a nitrogenatmosphere.

DETAILED DESCRIPTION

A pressure-sensitive adhesive is provided that is a dried product of alatex composition, which is formed from an emulsion composition. Thelatex composition and the emulsion composition are also provided. Theemulsion composition has droplets suspended in a first phase that ismainly water. The droplets contain various monomers plus a(meth)acrylate polymer dissolved in the monomers. The content of thedroplets in the emulsion composition are polymerized to form polymericlatex particles in the latex composition. A pressure-sensitive adhesiveis provided by drying the latex composition. Additionally, an articlecontaining a layer of the pressure-sensitive adhesive and a method offorming the pressure-sensitive adhesive are provided.

The pressure-sensitive adhesives often have a good balance between peelstrength and shear strength (i.e., cohesive strength or shear holdingpower), particularly when adhered to low surface energy surfaces. It canbe a challenge to make pressure-sensitive adhesives with this goodbalance of adhesive properties. Increasing the peel strength often isaccompanied by a decrease in shear strength while increasing the shearstrength often is accompanied by a decrease in peel strength. Theaddition of the second (meth)acrylate polymer into the emulsioncomposition contributed to the formation of pressure-sensitive adhesiveswith the improved balance between peel strength and sheer strength. Thatis, shear strength could be improved while maintaining good peelstrength (or without unduly sacrificing peel strength) and peel strengthcould be improved while maintaining good shear strength (or withoutunduly sacrificing shear strength).

As used herein, the terms “polymer” and “polymeric” and “polymericmaterial” are used interchangeably to refer to a homopolymer, copolymer,terpolymer, and the like.

As used herein, the term “(meth)acrylate” refers to both methacrylateand acrylate monomers, polymeric materials derived from these monomers,or both. Likewise, the term “(meth)acrylic” refers to both acrylic andmethacrylic materials, the term “(meth)acrylamide” refers to bothacrylamide and methacrylamide, and the term “(meth)acrylonitrile” refersto both methacrylonitrile and acrylonitrile.

As used herein, the term “(meth)acrylate polymer” refers to a polymericmaterial formed from one or more ethylenically unsaturated monomers,wherein greater than 50 weight percent of the monomers have anethylenically unsaturated group that is a (meth)acryloyl group offormula H₂C═CR^(a)—(CO)— where R^(a) is hydrogen or methyl and —(CO)— isa carbonyl group. Some example (meth)acrylate polymers are formed frommonomer compositions having greater than 60 weight percent, greater than70 weight percent, greater than 80 weight percent, greater than 90weight percent, greater than 95 weight percent, greater than 98 weightpercent, or greater than 99 weight percent monomers having a(meth)acryloyl group. The weight percent is based on the total weight ofmonomers in the monomer composition used to form the (meth)acrylatepolymer.

The term “glass transition temperature” or “T_(g)” refers to thetemperature at which a material changes from a glassy state to a rubberystate. In this context, the term “glassy” means that the material ishard and brittle (and therefore relatively easy to break) while the term“rubbery” means that the material is elastic and flexible. For polymericmaterials, the T_(g) is the critical temperature that separates theirglassy and rubbery behaviors. If a polymeric material is at atemperature below its T_(g), large-scale molecular motion is severelyrestricted because the material is essentially frozen. On the otherhand, if the polymeric material is at a temperature above its T_(g),molecular motion on the scale of its repeat unit takes place, allowingit to be soft or rubbery. Any reference herein to the T_(g) of a monomerrefers to the T_(g) of a homopolymer formed from that monomer. The glasstransition temperature of a polymeric material is often determined usingmethods such as Differential Scanning Calorimetry (e.g., ModulatedDifferential Scanning Calorimetry). Alternatively, the glass transitionof a polymeric material can be calculated using the Fox Equation if theamount and T_(g) of each monomer used to form the polymeric material areknown.

When referring to a range, the endpoints of the range are considered tobe in the range. For example, the expressions “in a range from x to y”,“in a range of x to y”, “in an amount from x to y”, “in an amount of xto y”, or similar expressions include the endpoints x and y.

As used herein, the term “and/or” such as in the expression A and/or Bmeans A alone, B alone, or both A and B.

The emulsion composition that is used to form the latex composition and,ultimately, the pressure-sensitive adhesive contains a) water, b) apolymerizable surfactant having an unsaturated group that can undergo afree radical polymerization reaction (e.g., an ethylenically unsaturatedgroup), c) a first monomer composition, and d) a second (meth)acrylatepolymer. The emulsion has a first phase that includes water and a secondphase dispersed as droplets within the first phase. The polymerizablesurfactant is typically predominately (e.g., at least 95 weight percentor more, at least 97 weight percent, at least 98 weight percent, atleast 99 weight percent, at least 99.5 weight percent, at least 99.8weight percent, or at least 99.9 weight percent) present in the firstphase and/or at the interface between the droplets and the first phase.The second (meth)acrylate polymer is dissolved in the monomers of thefirst monomer composition within the droplets of the second phase of theemulsion composition. The second (meth)acrylate polymer typically is notmiscible with the first phase of the emulsion composition. The second(meth)acrylate polymer is formed from a second monomer composition thatis different than the first monomer composition contained in theemulsion composition.

A major component of the emulsion composition is water. The percentsolids of the emulsion composition are often up to 70 weight percent orhigher such as up to 75 weight percent. If the percent solids arehigher, the viscosity of the emulsion may be too high to adequatelydisperse the droplets. In some embodiments, the percent solids are up to65 weight percent, up to 60 weight percent, up to 55 weight percent, orup to 50 weight percent. The percent solids are typically at least 10weight percent. If the solids are lower, the efficiency of preparationof the latex particles may be unacceptably low. In some embodiments, thepercent solids are at least 15 weight percent, at least 20 weightpercent, at least 25 weight percent, at least 30 weight percent, atleast 35 weight percent, at least 40 weight percent, or at least 45weight percent. In some examples, the percent solids are in a range of10 to 75 weight percent, 10 to 70 weight percent, 20 to 70 weightpercent, 30 to 70 weight percent, 40 to 70 weight percent, or 40 to 60weight percent. The percent solids are based on the total weight of theemulsion composition.

The portion of the emulsion composition that is not a solid is typicallywater. Thus, the water content of the emulsion is often at least 25weight percent or at least 30 weight percent. In some embodiments, thewater content can be up to 90 weight percent, up to 85 weight percent,up to 80 weight percent, up to 75 weight percent, up to 70 weightpercent, up to 65 weight percent, up to 60 weight percent, or up to 55weight percent. The water content can be at least 35 weight percent, atleast 40 weight percent, at least 45 weight percent, or at least 50weight percent. In some examples, the water content is in a range of 25to 90 weight percent, 30 to 90 weight percent, 30 to 80 weight percent,30 to 70 weight percent, 30 to 60 weight percent, or 40 to 60 weightpercent. The amount of water is based on the total weight of theemulsion composition.

Some of the water can be replaced with a polar organic solvent that ismiscible with water such as a polar solvent. If present, no more than 20weight percent, no more than 15 weight percent, no more than 10 weightpercent, or no more than 5 weight percent of the first phase is thewater-miscible, polar organic solvent. The polar solvent is often analcohol such as an alcohol having 1 to 10 carbon atoms, 1 to 6 carbonatoms, or 1 to 4 carbon atoms. In many embodiments, no water-miscible,polar organic solvent is purposefully added to the emulsion compositionbut may be present as a contaminant or diluent in one of the othercomponents.

The emulsion composition contains a polymerizable surfactant. As usedherein, the term “polymerizable surfactant” refers to a surfactant witha polymerizable group, which is an unsaturated group that can undergo afree radical polymerization reaction. In the emulsion composition, thepolymerizable surfactant is typically in the first phase and/or at theinterface between first phase and the droplets that are suspended in thefirst phase. The polymerizable surfactant facilitates the formation of alatex composition having good stability (e.g., the polymeric latexparticles remain suspended and do not coalesce). The polymerizablesurfactant may become part of the polymeric latex particles during thepolymerization reaction of the emulsion composition.

Using a polymerizable surfactant rather than a surfactant without apolymerizable group tends to improve the peel strength and the shearstrength of the resulting pressure-sensitive adhesive. Under highhumidity conditions, a surfactant without a polymerizable group tends tomigrate to the surface of a pressure-sensitive adhesive. The presence ofthe surfactant on the surface of the pressure-sensitive adhesive candecrease the adhesive properties of the pressure-sensitive adhesive. Incontrast, the polymerizable surfactant can polymerize with the monomersin the first monomer composition and become part of the polymeric latexparticles. Polymerization into the polymeric latex particle tends torestrict the mobility of the surfactant.

Example polymerizable surfactants include propenyl polyoxyethylenealkylphenyl compounds such as those commercially available fromMontello, Inc. (Tulsa, Okla., USA) under the trade designation NOIGEN RN(e.g., RN-10, RN-20, RN-30, RN-40, and RN-5065), which have a structureshown below where n is at least 2 and where x is an integer such as oneclose to or equal to 9.

Other example polymerizable surfactants include propenyl polyoxyethylenealkylphenyl ether ammonium sulfate compounds such as those commerciallyavailable from Montello, Inc. under the trade designation HITENOL BC(e.g., BC-10, BC-1025, BC-20, BC-2020, and BC-30), which have astructure shown below where n is at least 2 and where x is an integersuch as one close to or equal to 9.

Another example polymerizable surfactant is sodium dodecylallylsulfosuccinate, CH₃—(CH₂)₁₁—O—(CO)—CH₂—CH(SO₃Na)—(CO)—O—CH₂—CH═CH₂,which may be commercially available under the trade designation TREMLF40 from Cognis Corporation (North Rhime-Westphalia, Germany). Yetother example polymerizable surfactants are phosphate esters such asthose commercially available from Croda (Edison, N.Y., USA) under thetrade designation MAXENUL (e.g., MAXEMUL 6106 and 6112).

The polymerizable surfactant is typically used in an amount up to about2 weight percent, up to 1.8 weight percent, or up to 1.5 weight percent.The amount of the polymerizable surfactant is usually at least 0.5weight percent, at least 0.7 weight percent, or at least 1 weightpercent. The weight percents are based on the total weight of monomersin the first monomer composition.

The emulsion composition contains a first monomer composition. The firstmonomer composition is typically selected such that the polymerizedproduct of the first monomer composition, which is referred to as the“first (meth)acrylate polymer”, has a glass transition temperature nogreater than 20° C., no greater than 10° C., no greater than 0° C., nogreater than −10° C., or no greater than −20° C.

The first monomer composition in the emulsion composition typicallyincludes an alkyl (meth)acrylate having a linear or branched alkyl groupwith at least six carbon atoms. In many embodiments, other optionalmonomers can be included provided that the polymerized product has asufficiently low glass transition temperature. The amount and type ofany optional monomers are selected so that at least 90 weight percent ofthe monomers within the first monomer composition are within dropletsdispersed in the first phase of the emulsion composition. The alkyl(meth)acrylate monomer having a linear or branched alkyl group with atleast six carbon atoms is likely to have a low solubility in the firstphase and is likely to be predominately (e.g., at least 95 weightpercent or more, at least 97 weight percent, at least 98 weight percent,at least 99 weight percent, at least 99.5 weight percent, at least 99.8weight percent, or at least 99.9 weight percent) in the droplets, whichare dispersed in the first phase. If optional polar monomers or otheroptional monomers are included in the first monomer composition that areless hydrophobic that the alkyl (meth)acrylate monomer having a linearor branched alkyl group with at least six carbon atoms, the solubilityof these optional monomers may be greater in water (e.g., in the firstphase) compared to the alkyl (meth)acrylate monomer having a linear orbranched alkyl group with at least six carbon atoms. As polymerizationoccurs within the droplet, some of these optional monomers in the firstphase may diffuse into the droplet and become part of polymeric latexparticles that are formed.

The alkyl (meth)acrylate in the first monomer composition has a linearor branched alkyl group with at least six carbon atoms. Alkyl(meth)acrylate monomers with an alkyl group having less than six carbonatoms are less hydrophobic and are less likely to reside predominatelywithin the droplets. In some embodiments, the alkyl group can have atleast 8 carbon atoms, at least 10 carbon atoms, or at least 12 carbonatoms. The alkyl group of the alkyl (meth)acrylate can have up to 28carbon atoms or more, up to 24 carbon atoms, up to 20 carbon atoms, orup to 18 carbon atoms. In many embodiments, particularly when the numberof carbon atoms is greater than 12, the alkyl group is branched. Somealkyl (meth)acrylates having an alkyl group greater than 12 carbon atomscan crystallize if the alkyl group is linear. Crystallization of thealkyl (meth)acrylate is not desirable in the emulsion composition.

Example alkyl (meth)acrylate monomers having a linear or branched alkylgroup with at least six carbon atoms for use in the first monomercomposition include, but are not limited to, n-hexyl acrylate,4-methyl-2-pentyl acrylate, 3-methylpentyl acrylate, 2-ethylbutylacrylate, 2-ethylhexyl acrylate, 2-methylhexyl acrylate, n-octylacrylate, isooctyl acrylate, 2-octyl acrylate, isononyl acrylate,isoamyl acrylate, n-decyl acrylate, isodecyl acrylate, 2-propylheptylacrylate, isotridecyl acrylate, isostearyl acrylate, 2-octyldecylacrylate, lauryl acrylate, heptadecanyl acrylate, n-hexyl methacrylate,isodecyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate,and lauryl methacrylate.

Still others alkyl (meth)acrylates having a linear or branched alkylgroup with at least six carbon atoms for use in the first monomercomposition are of Formula (I).

In Formula (I), group R³ is hydrogen or methyl and groups R¹ and R² areeach independently a linear or branched alkyl group having 4 to 14carbon atoms. These monomers are often formed from a Guerbet alcohol,which is a 2-alkyl alkanol. Example monomers of Formula (I) include2-butyloctyl acrylate, 2-butyldecyl acrylate, 2-hexyloctyl acrylate,2-hexyldecyl acrylate, 2-tetradecyloctadecyl acrylate,2-dodecylhexadecyl acrylate, 2-decyltetradecyl acrylate, 2-octyldodecylacrylate, 2-hexyldecyl acrylate, 2-octyldecyl acrylate, 2-hexyldodecylacrylate, and 2-octyldodecyl acrylate.

The first monomer composition typically contains at least 50 weightpercent alkyl (meth)acrylate having a linear or branched alkyl groupwith at least six carbon atoms. The first monomer composition oftencontains at least 60 weight percent, at least 70 weight percent, or atleast 80 weight percent of the alkyl (meth)acrylate having a linear orbranched alkyl group with at least six carbon atoms. The amount of thealkyl (meth)acrylate having an alkyl group with at least six carbonatoms can be up to 100 weight percent. The first monomer compositionoften contains up to 95 weight percent, up to 90 weight percent, or upto 85 weight percent of the alkyl (meth)acrylate having a linear orbranched alkyl group with at least six carbon atoms. In someembodiments, the amount of the alkyl (meth)acrylate is in a range of 50to 100 weight percent, in a range of 50 to 95 weight percent, in a rangeof 60 to 95 weight percent, in a range of 70 to 95 weight percent, or ina range of 75 to 90 weight percent. The amount of the alkyl(meth)acrylate is based on a total weight of monomers in the firstmonomer composition.

In many embodiments, the alkyl (meth)acrylate having a linear orbranched alkyl group with at least six carbon atoms is combined with anoptional cyclic alkyl (meth)acrylate within the first monomercomposition. As used herein, the term “cyclic alkyl” refers to amono-cyclic alkyl, a bicyclic alkyl, or a tricyclic alkyl group.Examples of cyclic alkyl (meth)acrylate monomers include, but are notlimited to, isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl(meth)acrylate, cyclohexyl (meth)acrylate, adamantyl (meth)acrylate3,5-dimethyladamantyl (meth)acrylate, and 4-tert-butylcylcohexyl(meth)acrylate.

Some of these cyclic alkyl (meth)acrylates have a high glass transitiontemperature (such as at least 80° C.) and must be used in sufficientlylow amounts so that the polymerized product of the first monomercomposition has a glass transition temperature no greater than 20° C.The presence of the cyclic alkyl (meth)acrylate can enhance thesolubility of the second (meth)acrylate polymer within the first monomercomposition. In many embodiments that contain the optional cyclic alkyl(meth)acrylate, the first monomer composition contains at least 0.5weight percent, at least 1 weight percent, at least 2 weight percent, atleast 5 weight percent, or at least 10 weight percent of the cyclicalkyl (meth)acrylate. The amount of the cyclic alkyl (meth)acrylate canbe up to 30 weight percent, up to 25 weight percent, up to 20 weightpercent, or up to 15 weight percent. For example, the amount of thecyclic alkyl (meth)acrylate in the first monomer composition can be in arange of 0 to 30 weight percent, 1 to 30 weight percent, 0 to 20 weightpercent, 1 to 20 weight percent, or 5 to 20 weight percent. The weightpercent of the cyclic alkyl (meth)acrylate is based on a total weight ofmonomers in the first monomer composition.

The first monomer composition optionally can include a polar monomersuch as an optional acid-containing monomer (i.e., a monomer with anacidic group) or an optional hydroxyl-containing monomer (i.e., amonomer with a hydroxyl group). These optional monomers can be added toincrease the cohesive strength of the final polymeric material. Suitableoptional acid-containing monomers include, but are not limited to,(meth)acrylic acid, itaconic acid, maleic acid, 2-carboxyethyl acrylate,crotonic acid, citraconic acid, maleic acid, maleic anhydride (whichhydrolyzes to have two carboxylic acid groups), oleic acid, andmono-2-acryloyloxyethyl succinate. Suitable optional hydroxyl-containingmonomers include, but are not limited to, hydroxyalkyl (meth)acrylates(e.g., 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate), orhydroxyalkyl (meth)acrylamides (e.g., 2-hydroxyethyl (meth)acrylamide or3-hydroxypropyl (meth)acrylamide). In many embodiments, the polarmonomer is an acidic monomer. In many embodiments, the optional polarmonomer has a (meth)acryloyl group. The first monomer compositiontypically contains 0 to 15 weight percent, 0.5 to 15 weight percent, 1to 15 weight percent, 0 to 10 weight percent, 0.5 to 10 weight percent,1 to 10 weight percent, 0 to 5 weight percent, 0.5 to 5 weight percent,or 1 to 5 weight percent of the optional polar monomer. The amount ofthe optional polar monomer used is selected so that at least 85 weightpercent of the monomers in the first monomer composition are within thedroplets of the second phase. The weight percent is based on the totalweight of monomers within the first monomer composition.

The first monomer composition optionally can contain up to 20 weightpercent alkyl (meth)acrylate having an alkyl group with one to fivecarbon atoms. The alkyl group can be linear or branched. If largeramounts of an alkyl (meth)acrylate having an alkyl group with one tofive carbon atoms are used, too much of the overall first monomercomposition may be in the first phase rather than in the droplets. Inmany embodiments, the amount of alkyl (meth)acrylate having an alkylgroup with one to five carbon atoms is present in an amount no greaterthan 15 weight percent, no greater than 10 weight percent, or no greaterthan 5 weight percent. In some embodiments, there is no alkyl(meth)acrylate having an alkyl group with one to five carbon atoms. Inother embodiments, the first monomer composition can contain at least0.5 weight percent, at least 1 weight percent, at least 2 weightpercent, or at least 5 weight percent of the alkyl (meth)acrylate havingan alkyl group with one to five carbon atoms. The amount of the alkyl(meth)acrylate with an alkyl group having one to five carbon atoms isusually in a range of 0 to 20 weight percent, 1 to 20 weight percent, 5to 20 weight percent, 10 to 20 weight percent, 0 to 15 weight percent, 1to 15 weight percent, 5 to 15 weigh percent, 0 to 10 weight percent, 1to 10 weight percent, 0 to 5 weight percent, or 1 to 5 weight percent.The amount of the alkyl (meth)acrylate is based on a total weight ofmonomers in the first monomer composition.

The first monomer composition can contain 50 to 100 weight percent ofthe alkyl (meth)acrylate having a linear or branched alkyl group with atleast six carbon atoms, 0 to 30 weight percent of a cyclic alkyl(meth)acrylate, 0 to 20 weight percent of the alkyl (meth)acrylatehaving an alkyl group with one to five carbon atoms, and 0 to 15 weightpercent of a polar monomer. In some examples, the first monomercomposition contains 60 to 98 weight percent of the alkyl (meth)acrylatehaving a linear or branched alkyl group with at least six carbon atoms,1 to 25 weight percent of a cyclic alkyl (meth)acrylate, 0 to 15 weightpercent of the alkyl (meth)acrylate having an alkyl group with one tofive carbon atoms, and 1 to 15 weight percent of the polar monomer. Insome examples, the first monomer composition contains 70 to 98 weightpercent of the alkyl (meth)acrylate having a linear or branched alkylgroup with at least six carbon atoms, 1 to 20 weight percent of a cyclicalkyl (meth)acrylate, 0 to 10 weight percent of the alkyl (meth)acrylatehaving an alkyl group with one to five carbon atoms, and 1 to 10 weightpercent of the polar monomer.

In other examples, the first monomer composition contains 60 to 98weight percent of the alkyl (meth)acrylate having a linear or branchedalkyl group with at least six carbon atoms, 1 to 30 weight percent of acyclic alkyl (meth)acrylate, and 1 to 10 weight percent of the polarmonomer. For example, the first monomer composition contains 70 to 98weight percent of the alkyl (meth)acrylate having a linear or branchedalkyl group with at least six carbon atoms, 1 to 20 weight percent of acyclic (meth)acrylate, and 1 to 10 weight percent of the polar monomersuch as a (meth)acrylic acid.

The emulsion composition has droplets dispersed in the first phase.Prior to polymerization of the emulsion composition to form a latexcomposition, the droplets contain a solution of the second(meth)acrylate polymer dissolved in the components of the first monomercomposition that are in the droplets. Typically, at least 90 weightpercent of the monomers in the first monomer composition are within thedroplets of the emulsion and no more than 10 weight percent of themonomers of the first composition are within the first phase of theemulsion composition. Polar monomers or other monomers that are lesshydrophobic than the alkyl (meth)acrylate having a linear or branchedalkyl group with at least six carbon atoms may be distributed withinboth the droplets and the first phase. As polymerization proceeds, anyof these polar monomers or less hydrophobic monomers in the first phasemay diffuse into the droplets and become part of the polymeric latexparticles. In some embodiments, at least 92 weight percent, at least 95weight percent, at least 98 weight percent, or at least 99 weightpercent of the monomers in the first monomer composition are in thedroplets of the emulsion composition.

The second (meth)acrylate polymer is selected so that is can bedissolved in the first monomer composition within the droplets of theemulsion composition and so that it is not miscible with the firstphase. The second (meth)acrylate polymer is formed prior to dissolutionby the components of the first monomer composition within the droplets.The second (meth)acrylate polymer facilitates the formation of stabledroplets within the first phase of the emulsion composition.

The second (meth)acrylate polymer is typically formed from a secondmonomer composition. The second monomer composition is selected toprovide a second (meth)acrylate polymer that can be dissolved in thefirst monomer composition. The second monomer composition is notidentical to the first monomer composition. Additionally, it is oftendesirable that the second (meth)acrylate polymer be distributed fairlyuniformly throughout the droplets within the emulsion composition. Thatis, it is often desirable that the second (meth)acrylate polymer and thepolymeric material formed by polymerization of the first monomercomposition (i.e., the first (meth)acrylate polymer) are both fairlyuniformly distributed throughout the resulting polymeric latex particleseven though their compositions are not identical. The first(meth)acrylate polymer and the second (meth)acrylate polymer are withinthe same latex particles.

The second monomer composition is selected to provide a second(meth)acrylate polymer that has a glass transition temperature that isat least 50° C. as measured using Differential Scanning Calorimetry(e.g., Modulated Differential Calorimetry). For example, the glasstransition temperature is at least 60° C., at least 70° C., at least 80°C., at least 90° C., or at least 100° C. The glass transitiontemperature can be up to 250° C., up to 200° C., or up to 175° C. Often,the glass transition temperature is no greater than 150° C., no greaterthan 140° C., no greater than 130° C., or no greater than 120° C.

The second monomer composition usually includes at least 50 weightpercent of a cyclic alkyl (meth)acrylate based on a total weight ofmonomers in the second monomer composition, wherein the cyclic group hasat least six carbon atoms. For example, the cyclic group can have up to12 carbon atoms, up to 10 carbon atoms, or up to 8 carbon atoms.Examples of cyclic alkyl (meth)acrylate monomers include, but are notlimited to, isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl(meth)acrylate, cyclohexyl (meth)acrylate, adamantyl (meth)acrylate,3,5-dimethyladamantyl (meth)acrylate, and 4-tert-butylcylcohexyl(meth)acrylate.

In many embodiments, the cyclic alkyl (meth)acrylate has a glasstransition temperature that is at least 80° C. when polymerized as ahomopolymer. Suitable monomers include, but are not limited to,isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl methacrylate,cyclohexyl methacrylate, 3,5-dimethyladamantyl acrylate, and4-tert-butylcylcohexyl methacrylate.

The cyclic alkyl (meth)acrylate can be the only monomer in the secondmonomer composition or it can be combined with other optional monomersprovided that 1) the resulting second (meth)acrylate polymer has a glasstransition temperature equal to at least 50° C. as measured usingDifferential Scanning Calorimetry (e.g., Modulated Differential ScanningCalorimetry), 2) the resulting second (meth)acrylate polymer can bedissolved in the first monomer composition, and 3) the second(meth)acrylate polymer remains within the droplets of the emulsioncomposition and is not miscible with the first phase of the emulsioncomposition. These optional monomers include, for example, a polarmonomer, an alkyl (meth)acrylate having a linear or branched alkylgroup, (meth)acrylamide, a (meth)acrylonitrile, an N-alkyl(meth)acrylamide, an N,N-dialkyl (meth)acrylamide, and a vinyl monomerthat does not have a (meth)acryloyl group.

The second monomer composition can optionally include a polar monomersuch as an optional acid-containing monomer (i.e., a monomer with anacidic group) or an optional hydroxyl-containing monomer (i.e., amonomer with a hydroxyl group). Suitable optional acid-containingmonomers include, but are not limited to, (meth)acrylic acid, itaconicacid, maleic acid, 2-carboxyethyl acrylate, crotonic acid, citraconicacid, maleic acid, maleic anhydride (which hydrolyzes to have twocarboxylic acid groups), oleic acid, and mono-2-acryloyloxyethylsuccinate. Suitable optional hydroxyl-containing monomers include, butare not limited to, hydroxyalkyl (meth)acrylates (e.g., 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl(meth)acrylate, and 4-hydroxybutyl (meth)acrylate), or hydroxyalkyl(meth)acrylamides (e.g., 2-hydroxyethyl (meth)acrylamide or3-hydroxypropyl (meth)acrylamide). In many embodiments, the optionalpolar monomer has a (meth)acryloyl group. In many embodiments, theoptional polar monomer is (meth)acrylic acid. The second monomercomposition typically contains 0 to 10 weight percent, 1 to 10 weightpercent, 0 to 5 weight percent, or 1 to 5 weight percent of the optionalacid-containing monomer and/or optional hydroxyl-containing monomer. Theweight percent values are based on the total weight of monomers withinthe second monomer composition.

The second monomer composition can optionally include an alkyl(meth)acrylate having a linear or branched alkyl group. Example monomersinclude methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl(meth)acrylate, isobutyl (meth)acrylate, n-butyl (meth)acrylate,tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl(meth)acrylate, 2-methylbutyl (meth)acrylate, n-hexyl (meth)acrylate,4-methyl-2-pentyl (meth)acrylate, 2-methylhexyl (meth)acrylate,2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-octyl(meth)acrylate, 2-octyl (meth)acrylate, isononyl (meth)acrylate, isoamyl(meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate,2-propylheptyl (meth)acrylate, isotridecyl (meth)acrylate, and lauryl(meth)acrylate. The amount of the alkyl methacrylate is often limited bythe desired glass transition temperature of the second (meth)acrylatepolymer.

Other suitable optional monomers for use in second monomer compositioninclude (meth)acrylamide, (meth)acrylonitrile, an N-alkyl(meth)acrylamide having an alkyl group with 1 to 10 carbon atoms (e.g.,2 to 10 carbon atoms or 4 to 10 carbon atoms) such as N-octylacrylamide, N-isopropyl acrylamide, or N-tert-butyl acrylamide, or anN,N-dialkyl (meth)acrylamide having alkyl groups with 1 to 10 carbonatoms (e.g., 1 to 6 carbon atoms or 1 to 4 carbon atoms) such asN,N-dimethyl acrylamide.

Still other optional monomers can be included in the second monomercomposition provided that there is suitable compatibility between theresulting second (meth)acrylate polymer and first monomer compositionwithin the emulsion composition and provided that the second(meth)acrylate polymer can be dissolved within the droplets of theemulsion composition. Examples of other optional monomers includevarious vinyl monomers, wherein the vinyl group is not a (meth)acryloylgroup. Optional vinyl monomers include, for example, vinyl esters suchas vinyl butyrate, and various vinyl non-aromatic heterocyclic monomerssuch as N-vinyl pyrollidone and N-vinyl caprolactam.

A crosslinking monomer typically is not included in the second monomercomposition. A crosslinked (meth)acrylate polymer would be difficult todissolve in the first monomer composition. In many embodiments, thesecond monomer composition does not contain an aromatic monomer (i.e., amonomer with an aromatic group such as a styrenic monomer or aryl(meth)acrylate).

In many embodiments, the second monomer composition includes 50 to 100weight percent of a cyclic alkyl (meth)acrylate and 0 to 50 percentoptional monomers such as those selected from a polar monomer, an alkyl(meth)acrylate having a linear or branched alkyl group, and a vinylmonomer that does not have a (meth)acryloyl group, (meth)acrylamide,(meth)acrylonitrile, N-alkyl (meth)acrylamide, N,N-dialkyl(meth)acrylamide, and a mixture thereof. For example, the second monomercomposition can include 60 to 100 weight percent of the cyclic alkyl(meth)acrylate and 0 to 40 percent optional monomers, 70 to 100 weightpercent of the cyclic alkyl (meth)acrylate and 0 to 30 percent optionalmonomers, 80 to 100 weight percent of the cyclic alkyl (meth)acrylateand 0 to 20 percent optional monomers, 90 to 100 weight percent of thecyclic alkyl (meth)acrylate and 0 to 10 percent optional monomers, 90 to99 weight percent of the cyclic alkyl (meth)acrylate and 1 to 10 percentoptional monomers, 95 to 100 weight percent of the cyclic alkyl(meth)acrylate and 0 to 5 percent optional monomers, or 95 to 99 weightpercent of the cyclic alkyl (meth)acrylate and 1 to 5 percent optionalmonomers. The weight percents are based on the total weight of monomerswithin the second monomer composition.

In some more specific embodiments, the second monomer compositioncontains 1) 50 to 100 weight percent of the cyclic alkyl (meth)acrylate,2) 0 to 50 weight percent of a second monomer selected from an alkyl(meth)acrylate having a linear or branched alkyl group, and a vinylmonomer that does not have a (meth)acryloyl group, (meth)acrylamide,(meth)acrylonitrile, N-alkyl (meth)acrylamide, and N,N-dialkyl(meth)acrylamide, and 3) 0 to 10 weight percent of a polar monomer. Forexample, the second monomer composition contains 1) 50 to 99 weightpercent of the cyclic alkyl (meth)acrylate, 2) 0 to 50 weight percent ofthe second monomer, and 3) 1 to 10 weight percent of a polar monomer;or 1) 50 to 99 weight percent of the cyclic alkyl (meth)acrylate, 2) 0to 40 weight percent of the second monomer, and 3) 1 to 10 weightpercent of a polar monomer; or 1) 70 to 99 weight percent of the cyclicalkyl (meth)acrylate, 2) 0 to 20 weight percent of the second monomer,and 3) 1 to 10 weight percent of a polar monomer.

In some particular embodiments, the second monomer composition contains90 to 99 weight percent of the cyclic alkyl (meth)acrylate and 1 to 10percent polar monomer, 95 to 100 weight percent of the cyclic alkyl(meth)acrylate and 0 to 5 percent polar, or 95 to 99 weight percent ofthe cyclic alkyl (meth)acrylate and 1 to 5 percent polar. The weightpercents are based on the total weight of monomers within the secondmonomer composition. In many embodiments, the polar monomer is anacid-containing monomer such as, for example, a (meth)acrylic acid.

In addition to the second monomer composition, the polymerizablecomposition used to form the second (meth)acrylate polymer oftencontains a chain transfer agent. The chain transfer agent is used tocontrol the molecular weight of the second (meth)acrylate polymer.Examples of useful chain transfer agents include, but are not limitedto, carbon tetrabromide, alcohols (e.g., ethanol and isopropanol),thiols (e.g., lauryl mercaptan, butyl mercaptan, ethanethiol,isooctylthioglycolate, 2-ethylhexyl thioglycolate, 2-ethylhexylmercaptopropionate, ethyleneglycol bisthioglycolate), and mixturesthereof. In many embodiments, the preferred chain transfer agent isiso-octyl thioglycolate (IOTG), carbon tetrabromide,tert-dodecylmercaptan (TDDM), or n-dodecylmercaptan. The amount of theoptional chain transfer agent is often in a range of 0 to 5 weightpercent based on the total weight of monomers in the second monomercomposition. If present, the chain transfer agent is often used in anamount of at least 0.01 weight percent, at least 0.02 weight percent, atleast 0.05 weight percent, or at least 0.1 weight percent. The amountcan be up to 5 weight percent, up to 3 weight percent, up to 2 weightpercent, up to 1 weight percent, or up to 0.5 weight percent.

Other optional components can be added along with the second monomercomposition to the polymerizable composition used to form the highsecond (meth)acrylate polymer. For example, the polymerizablecomposition can include an inhibitor and/or antioxidant. Suitableinhibitors and/or antioxidants include, but are not limited to,mono-methyl ether of hydroquinone (MEQH) and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), which iscommercially available from BASF (Florham Park, N.J., USA) under thetrade designation IRGANOX 1010.

The polymerizable composition used to form the second (meth)acrylatepolymer typically includes a free radical initiator to commencepolymerization of the monomers. The free radical initiator can be aphotoinitator or a thermal initiator. The free radical initiator istypically present in an amount up to 5 weight percent based on the totalweight of the monomers in the second monomer composition. In someembodiments, the amount of free radical initiator is up to 4 weightpercent, up to 3 weight percent, up to 2 weight percent, or up to 1weight percent. The amount of free radical initiator included in thepolymerizable composition is typically at least 0.005 weight percent.For example, the polymerizable composition often contains at least 0.01weight percent, at least 0.02 weight percent, at least 0.05 weightpercent, at least 0.1 weight percent, at least 0.2 weight percent, or atleast 0.5 weight percent free radical initiator.

Suitable thermal initiators include various azo compound such as thosecommercially available under the trade designation VAZO from E. I.DuPont de Nemours Co. (Wilmington, Del., USA) including VAZO 67, whichis 2,2′-azobis(2-methylbutane nitrile), VAZO 64, which is2,2′-azobis(isobutyronitrile), VAZO 52, which is2,2′-azobis(2,4-dimethylpentanenitrile), and VAZO 88, which is1,1′-azobis(cyclohexanecarbonitrile); various peroxides such as benzoylperoxide, cyclohexane peroxide, lauroyl peroxide, di-tert-amyl peroxide,tert-butyl peroxy benzoate, di-cumyl peroxide, and peroxidescommercially available from Atofina Chemical, Inc. (Philadelphia, Pa.,USA) under the trade designation LUPERSOL (e.g., LUPERSOL 101, which is2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, and LUPERSOL 130, which is2,5-dimethyl-2,5-di-(tert-butylperoxy)-3-hexyne); various hydroperoxidessuch as tert-amyl hydroperoxide and tert-butyl hydroperoxide; andmixtures thereof.

In some embodiments, a photoinitiator is used. Some exemplaryphotoinitiators are benzoin ethers (e.g., benzoin methyl ether orbenzoin isopropyl ether) or substituted benzoin ethers (e.g., anisoinmethyl ether). Other exemplary photoinitiators are substitutedacetophenones such as 2,2-diethoxyacetophenone or2,2-dimethoxy-2-phenylacetophenone (commercially available under thetrade designation IRGACURE 651 from BASF Corp. (Florham Park, N.J., USA)or under the trade designation ESACURE KB-1 from Sartomer (Exton, Pa.,USA)). Still other exemplary photoinitiators are substitutedalpha-ketols such as 2-methyl-2-hydroxypropiophenone, aromatic sulfonylchlorides such as 2-naphthalenesulfonyl chloride, and photoactive oximessuch as 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime. Othersuitable photoinitiators include, for example, 1-hydroxycyclohexylphenyl ketone (commercially available under the trade designationIRGACURE 184), bis(2,4,6-trimethylbenzoyl)phenylphosphineoxide(commercially available under the trade designation IRGACURE 819),1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one(commercially available under the trade designation IRGACURE 2959),2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone (commerciallyavailable under the trade designation IRGACURE 369),2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (commerciallyavailable under the trade designation IRGACURE 907), and2-hydroxy-2-methyl-1-phenyl propan-1-one (commercially available underthe trade designation DAROCUR 1173 from Ciba Specialty Chemicals Corp.(Tarrytown, N.Y., USA)).

Additionally, an organic solvent can be added, if desired, to controlthe viscosity of the polymerizable composition used to form the second(meth)acrylate polymer. The amount of organic solvent, if any, istypically determined by the polymerization method. In some solvent-basedpolymerization methods, the polymerizable composition can contain up to70 weight percent organic solvent. For adiabatic polymerization methods,however, the amount of organic solvent is typically no greater than 10weight percent, no greater than 8 weight percent, no greater than 5weight percent, no greater than 3 weight percent, or no greater than 1weight percent of the polymerizable composition. Any organic solventused in the polymerizable composition is typically removed at thecompletion of the polymerization reaction. Suitable organic solventsinclude, but are not limited to, methanol, tetrahydrofuran, ethanol,isopropanol, heptane, acetone, methyl ethyl ketone, methyl acetate,ethyl acetate, toluene, xylene, and ethylene glycol alkyl ether. Thosesolvents can be used alone or as mixtures thereof. In many embodiments(such in some adiabatic polymerization processes), the polymerizationoccurs with little or no organic solvent present.

The monomers used to form the second (meth)acrylate polymer can bepolymerized using any suitable method such as, for example, solution(i.e., with a solvent) polymerization, dispersion polymerization,suspension polymerization, and solventless polymerization (for example,bulk polymerization with either UV or thermal initiator). Thepolymerization can occur in a single step or in multiple steps. That is,all or a portion of the polymerizable composition may be charged into asuitable reaction vessel and polymerized. If multiple steps are used, aninitial charge of monomers and initiator are added to the reactor. Afterpolymerization of the initial charge, another portion of any remainingmonomers and/or initiator are added. Multiple polymerization steps canhelp narrow the polydispersity of the polymerized product (e.g., theamount of low molecular weight chains can be reduced), can help minimizeor control the heat of reaction, and can allow for adjustment of thetype and amount of monomer available during polymerization.

In many embodiments, the second (meth)acrylate polymer is not formedusing emulsion or dispersion polymerization methods. Rather, the second(meth)acrylate polymer is prepared using a solventless bulkpolymerization method or a solution polymerization method. Either athermal initiator or a photoinitiator can be used. In some embodiments,polymerization occurs using an adiabatic process as described, forexample, in U.S. Pat. No. 5,986,011 (Ellis et al.) and U.S. Pat. No.5,637,646 (Ellis). A thermal initiator is used with this process.

The weight average molecular weight of the second (meth)acrylate polymeris typically at least 3,000 grams/mole. If the weight average molecularweight is lower, the resulting pressure-sensitive adhesive may have anunacceptably low cohesive strength. The second (meth)acrylate polymeroften has a weight average molecular weight of at least 5,000grams/mole, at least 10,000 grams/mole, or at least 20,000 grams/mole.The weight average molecular weight can be up to 150,000 grams/mole. Ifthe molecular weight is higher, the second (meth)acrylate polymer mightnot dissolve in the first monomer composition of the emulsioncomposition. If not dissolved in the first monomer composition, thesecond (meth)acrylate polymer can undesirably be present in separatedroplets from the first monomer composition within the emulsioncomposition and/or can phase separate during polymerization. The weightaverage molecular weight is often up to 120,000 grams/mole, up to100,000 grams/mole, up to 80,000 grams/mole, up to 60,000 grams/mole, orup to 50,000 grams/mole. For example, the weight average molecularweight can be in a range of 3,000 to 150,000 grams/mole, in the range of10,000 to 150,000 grams/mole, in a range of 3,000 to 100,000 grams/mole,in the range of 10,000 to 100,000 grams/mole, in a range of 3,000 to50,000 grams/mole, or in the range of 10,000 to 50,000 grams/mole.

The second (meth)acrylate polymer is added to the emulsion composition.That is, this polymeric material is prepared prior to combination withthe other components of the emulsion composition. The second(meth)acrylate polymer typically does not undergo further free radicalpolymerization within the emulsion composition or with other componentsof the emulsion composition. The second (meth)acrylate can, however,undergo a crosslinking reaction within the emulsion composition.

The second (meth)acrylate polymer is usually added to the emulsioncomposition after being dissolved in the first monomer composition. Thatis, a solution containing the second (meth)acrylate polymer and thefirst monomer composition are added together to the first phase of theemulsion. The solution is typically added under conditions of high shearmixing to form droplets suspended within the first phase. In someembodiments, the second (meth)acrylate polymer is initially dissolved ina portion of the first monomer composition and then the resultingpolymer solution is then mixed with the remaining monomers of the firstmonomer composition.

The amount of second (meth)acrylate polymer added to the emulsioncomposition is typically at least 0.5 weight percent or at least 1weight percent. If a lower amount of the second (meth)acrylate polymeris added, the stability of the emulsion composition may be poor. Thatis, it can be difficult to form and maintain droplets in the emulsioncomposition. In some embodiments, the emulsion composition contains atleast 2 weight percent, at least 3 weight percent, or at least 5 weightpercent of the second (meth)acrylate polymer. The amount of the second(meth)acrylate polymer added is typically up to 15 weight percent. If ahigher amount of the second (meth)acrylate polymer is added, thepolymerization of the first monomer composition within the droplets maybe undesirably slow. Additionally, the polymeric material formed fromthe first monomer composition may have an undesirably low molecularweight and the resulting pressure-sensitive adhesive may have anundesirably low cohesive strength. In some embodiments, the emulsioncomposition contains up to 12 weight percent, up to 10 weight percent,or up to 8 weight percent of the second (meth)acrylate polymer. Theweight percents are based on a total weight of the first monomercomposition in the emulsion composition (i.e., the total weight ofmonomers in the first monomer composition).

The emulsion composition contains both the first monomer composition andthe second (meth)acrylate polymer within the same droplets. Morespecifically, the emulsion composition often contains 0.5 to 15 weightpercent of the second (meth)acrylate polymer and 85 to 99.5 weightpercent first monomer composition based on the total weight of thesecond (meth)acrylate polymer plus the weight of monomers in the firstmonomer composition (this does not include the small amount ofpolymerizable surfactant). This is the total polymerized andpolymerizable material in the emulsion composition. Most of thispolymerized and polymerizable material are present within the dropletsof the emulsion (e.g., some of the acidic monomers may be dissolved inthe first phase). In some examples, the emulsion composition can contain1 to 15 weight percent of the second (meth)acrylate polymer and 85 to 99weight percent of the first monomer composition, 2 to 12 weight percentof the second (meth)acrylate polymer and 88 to 98 weight percent firstmonomer composition, 2 to 10 weight percent of the second (meth)acrylatepolymer and 90 to 98 weight percent first monomer composition, or 2 to 8weight percent of the second (meth)acrylate polymer and 92 to 98 weightpercent first monomer composition based on the total weight of thesecond (meth)acrylate polymer plus the weight of monomers in the firstmonomer composition.

In some particular embodiments, the first monomer composition contains amixture of one or more alkyl (meth)acrylates having a linear or branchedalkyl group with at least six carbon atoms, one or more cyclic alkyl(meth)acrylates, and one or more (meth)acrylic acids. The second(meth)acrylate is formed from a second monomer composition that containsone or more cyclic alkyl (meth)acrylates and one or more (meth)acrylicacids.

Other optional reactants can be included in the emulsion composition.For example, in some embodiments, a crosslinker is added that can reactwith multiple carboxylic acid groups (—COOH). The carboxylic acid groupscan be on the second (meth)acrylate polymer, on the polymeric materialformed from the first monomer composition, or on a combination of bothpolymeric materials. The use of the optional crosslinkers may increasethe shear strength of the resulting pressure-sensitive adhesive.

Suitable crosslinkers capable of reacting with multiple carboxylic acidgroups include, but are not limited to, polyoxazolines such as thosecommercially available under the trade designation EPOCROS from NipponShokubai Co., LTD (Japan), polyaziridines (e.g., trimehtylolpropanetris(2-methyl-1aziridine propionate from PolyAziridine LCC (Medford,N.J., USA)), polyamines, or the like. Other suitable crosslinkersinclude metal salts that can complex with multiple carboxylic acidgroups. Suitable metals include, for example, zinc salts. If used, theoptional crosslinker is often added in an amount equal to at least 0.01weight percent based on the total weight of monomers in the firstmonomer composition. For example, the emulsion can contain at least 0.05weight percent, at least 0.1 weight percent, or at least 0.5 weightpercent of the crosslinker. The amount of the optional crosslinker isoften up to 3 weight percent based on the total weight of monomers inthe first monomer composition. For example, the emulsion composition cancontain up to 2.5 weight percent, up to 2 weight percent, up to 1.5weight percent, or up to 1 weight percent of the optional crosslinker.

In many embodiments, an optional neutralizing agent is added to theemulsion composition. The neutralizing agent can be added, for example,to improve the reactivity of the crosslinker, to improve the stabilityof the resulting latex composition, or the like. Suitable neutralizingagents are often strong or weak bases such as, for example, ammoniumhydroxide, ammonia, sodium acetate, potassium acetate, sodium hydroxide,potassium hydroxide, and lithium hydroxide. The neutralizing agent isoften added to increase the pH of the emulsion composition to at least4.0, at least 4.5, at least 5.0, at least 5.5, at least 6.0, at least6.5, or at least 7.0.

The emulsion composition typically further includes an initiator. Whileeither a water soluble or oil soluble initiator can be used, theinitiator is typically selected to be soluble in water. If the initiatoris oil soluble, it is typically added to the mixture (solution) ofmonomers of the first monomer composition and the second (meth)acrylatepolymer before this mixture (solution) is combined with the first phaseof the emulsion composition. If the initiator is water soluble, it isoften added after formation of the droplets within the first phase ofthe emulsion composition. If a reducing agent is used, it is usuallywater soluble and is added to the first phase.

Examples of water soluble initiators include, but are not limited to,hydrogen peroxide and various persulfate salts such as sodiumpersulfate, potassium persulfate, and ammonium persulfate. Optionalreducing agents can be added to lower the temperature needed forinitiation of the polymerization reaction. Suitable reducing agentsinclude, but are not limited to, ascorbic acid, bisulfite salts (e.g.,sodium bisulfite, potassium bisulfite, and ammonium bisulfite), andsodium formaldehyde sulfoxylate. The amount of initiator and optionalreducing agent can each be up to 1 weight percent based on the weight ofmonomers in the first monomer composition. For example, the amounts canbe up to 0.8 weight percent, up to 0.5 weight percent, up to 0.3 weightpercent, or up to 0.2 weight percent based on a total weight of monomersin the first monomer composition. The amount is initiator and optionalreducing agent each can be at least 0.01 weight percent, at least 0.05weight percent, or at least 0.1 weight percent based on the total weightof monomers in the first monomer composition.

Examples of oil soluble initiators include, but are not limited to, azocompounds or peroxides such as those mentioned above for the formationof the second (meth)acrylate polymer. If such initiators are used, theyare used in the same amount as described above for water solubleinitiators.

In many emulsion compositions, a chain transfer agent is not used. Asdescribed above, however, a chain transfer agent can be used (andusually is used) in the formation of the second (meth)acrylate polymer.

The emulsion composition does not include a tackifier.

The emulsion composition can be prepared by any suitable process thatresults in the formation of droplets containing the second(meth)acrylate polymer dissolved in monomers of the first monomercomposition. In many embodiments, the second (meth)acrylate polymer isinitially mixed with monomers included in the first monomer composition.The monomers are often used in their neat form without the addition ofany solvent. Once the second (meth)acrylate polymer has dissolved, themixture (solution) is combined with water or with water and othercomponents of the emulsion composition using high shear mixing. In someembodiments, the polymerizable surfactant and neutralizing agent can bedissolved in (or combined with) the water prior to mixing.

With high shear mixing, droplets form within the first phase (i.e.,aqueous phase). Prior to any polymerization of the first monomercomposition, the droplets contain a mixture of i) the second(meth)acrylate polymer and ii) at least 90 weight percent of the firstmonomer composition, wherein the second (meth)acrylate polymer isdissolved in the first monomer composition within the droplets.Typically, the droplets include at least 92 weight percent, at least 95weight percent, at least 97 weight percent, at least 98 weight percent,or at least 99 weight percent of the monomers in the first monomercomposition. The polymerizable surfactant is likely to be at theinterface between the droplets and the first phase or dissolved in firstphase. Most of the polymerizable surfactant is likely to be at theinterface. In many embodiments, any initiator, and/or reducing agent,and/or neutralizing agent included in the emulsion composition arelikely to be dissolved in the first phase.

The droplets suspended in the first phase typically have an averagediameter up to about 2000 nanometers, up to 1500 nanometers, up to 1000nanometers, up to 900 nanometers, up to 800 nanometers, up to 700nanometers, up to 600 nanometers, or up to 500 nanometers. The averagediameter is typically at least 100 nanometers, at least 200 nanometers,at least 300 nanometers, or at least 400 nanometers. The average sizecan be determined using dynamic light scattering methods. In someembodiments, the average droplet size (diameter) is in a range of 100 to2000 nanometers, in a range of 200 to 1000 nanometers, in a range of 300to 1000 nanometers, in a range of 200 to 800 nanometers, or in a rangeof 400 to 700 nanometers.

In many embodiments, the emulsion composition is considered to be amini-emulsion. As used herein, the term “mini-emulsion” refers to anemulsion method that uses high shear to make droplets having an averagediameter no greater than 1 micrometer. Polymerization occurs within thedroplets to form polymeric latex particles. Polymerization is limited tothat which occurs within the droplets.

The first monomer composition is typically polymerized at roomtemperature (e.g., about 20° C. to about 25° C.) or at a temperatureabove room temperature. The temperature is often at least 30° C., atleast 40° C., or at least 50° C. The temperature can be up to theboiling temperature of the emulsion composition (e.g., about 100° C.).In some embodiments, the temperature can be up to 80° C., up to 70° C.,or up to 60° C. Any heat generated during polymerization is rapidlymoderated by the effect of the heat capacity of the first phase. Thereaction time can be any length of time needed to complete thepolymerization reaction. In some embodiments, the reaction time can beat least 1 hour, at least 2 hours, at least 3 hours, or at least 4hours. The reaction time is up to 24 hours or longer, up to 16 hours, orup to 8 hours. The reactor is often purged with an inert gas such asnitrogen.

The polymerized product of the emulsion composition is a latexcomposition. That is, the latex composition contains water and polymericparticles that are a polymerized product of the emulsion composition asdescribed above. The terms “latex” and “latex composition” may be usedinterchangeably. The terms “polymeric particle” and “latex particles”and “polymeric latex particles” may be used interchangeably. Both i) thesecond (meth)acrylate polymer plus ii) the polymerized product of thefirst monomer composition (the first (meth)acrylate polymer) are presentwithin the same latex particles. The latex composition contains latexparticles having an average size comparable to the average size of thedroplets within the emulsion composition prior to polymerization. Moreparticularly, the average particle size of the latex particles isroughly equal to or slightly larger than the average droplet size withinthe emulsion composition due to density differences.

The latex particles are typically suspended (e.g., dispersed) in thewater phase (first phase). Preferably, the latex particles are notcoagulated together. The latex particles include both the second(meth)acrylate polymer and the first (meth)acrylate polymer. Themolecular weight of the first (meth)acrylate polymer is typically higherthan the molecular weight of polymeric materials of the same overallchemical composition formed using other processes. More specifically,the molecular weight of the first (meth)acrylate polymer formed byemulsion polymerization can be close to 1 million Daltons.

In contrast to the emulsion polymerization method used to form the first(meth)acrylate polymer, a typical molecular weight of polymers formedfrom the same monomers using solution polymerization or bulkpolymerization methods is often less than 500,000 Daltons. With bothsolution polymerization and bulk polymerization methods, the molecularweight is usually controlled by the initiator concentration. That is,higher initiator concentrations tend to produce lower molecular weightpolymers. Therefore, in order to produce high molecular weight polymersusing solution polymerization or bulk polymerization methods, extremelylow initiator concentrations are required. However, if extremely lowinitiator concentrations are used, the polymerization time may beunacceptably long. Such processes may be economically impractical toprepare high molecular weight polymeric materials. The high molecularweight polymeric materials, however, are often desirable for someadhesive applications such as where high shear strength is necessary.

With emulsion polymerization methods, the molecular weight of thepolymeric material (e.g., the molecular weight of the first(meth)acrylate polymer) can be controlled by both initiatorconcentration and the number of particles (i.e., number of droplets inthe emulsion). Higher initiator concentrations often result in lowermolecular weights and faster reaction times. Higher particle numbers,however, tend to favor higher molecular weights and faster reactiontimes.

Due to the high molecular weight of the polymeric materials formed fromemulsion compositions, crosslinking structures can often form moreeasily compared to polymeric materials formed using solutionpolymerization and bulk polymerization methods even in the absence ofadditional crosslinkers. Two possible types of crosslinking can occur inthe polymeric materials formed by emulsion polymerization: 1) physicalentanglement and 2) chemical crosslinking due to the chain transferreactions to a polymeric chain. Physical entanglement can be enhancedwith longer polymeric chains resulting from the increased averagemolecular weight. Chain transfer reactions can form crosslinkingstructures for long polymeric chains.

The latex particles typically have a single glass transition temperatureas determined using a Differential Scanning Calorimeter. Morespecifically, there is a single peak in the plot of reversible heat flowversus temperature for the dry polymeric material (dry polymeric latexparticles) during the second heating cycle using Modulated DifferentialScanning Calorimetry. The T_(g) is typically no greater than 0° C., nogreater than −10° C., or no greater than −20° C.

The latex composition can be combined with an optional tackifier. Theaddition of a tackifier can be used to increase adhesion. Any suitabletackifier can be used such as rosin acids and their derivatives (e.g.,rosin esters); terpene resins such as polyterpenes (e.g., alphapinene-based resins, beta pinene-based resins, and limonene-basedresins, and aromatic-modified polyterpene resins (e.g., phenol modifiedpolyterpene resins)); coumarone-indene resins; and petroleum-basedhydrocarbon resins such as C5-based hydrocarbon resins, C9-basedhydrocarbon resins, C5/C9-based hydrocarbon resins, anddicyclopentadiene-based resins. These tackifying resins, if added, canbe hydrogenated to lower their color contribution to thepressure-sensitive adhesive composition. Combinations of varioustackifiers can be used, if desired.

In many embodiments, the tackifier is a rosin ester or includes a rosinester. Tackifiers that are rosin esters are the reaction products ofvarious rosin acids and alcohols. These include, but are not limited to,methyl esters of rosin acids, triethylene glycol esters of rosin acids,glycerol esters of rosin acids, and pentaertythritol esters of rosinacids. These rosin esters can be hydrogenated partially or fully toimprove stability and reduce their color contribution to thepressure-sensitive adhesive composition. The rosin resin tackifiers arecommercially available, for example, from Eastman Chemical Company(Kingsport, Tenn., USA) under the trade designations PERMALYN,STAYBELITE, and FORAL as well as from Newport Industries (London,England) under the trade designations NUROZ and NUTAC. A fullyhydrogenated rosin resin is commercially available, for example, fromEastman Chemical Company under the trade designation FORAL AX-E. Apartially hydrogenated rosin resin is commercially available, forexample, from Eastman Chemical Company under the trade designationSTAYBELITE-E.

Often, it is desirable to use a tackifier that can be dispersed inwater. Water dispersion of rosin esters are available under the tradedesignation SNOWTACK from Lawter, Inc. (Chicago, Ill., USA). Othersuitable water dispersed tackifiers are commercially available under thetrade designation TACOLYN from Eastman Chemical Company that include,for example, rosin ester resin dispersions, hydrogenated rosin esterresin dispersions, aliphatic hydrocarbon resin dispersions, and aromaticmodified hydrocarbon resin dispersion.

If present, the optional tackifier in the latex composition is oftenused in an amount in a range of 1 to 40 weight percent based on thetotal weight of the polymeric latex particles. In some embodiments, theamount of tackifier is at least 5 weight percent, or at least 10 weightpercent and can be up to 35 weight percent, up to 30 weight percent, upto 25 weight percent, or up to 20 weight percent.

Other optional components that can be added to the latex composition arethickeners. Example thickeners are typically aqueous polymer solutionssuch as those available under the trade designation PARAGUM from RoyalCoatings and Specialty Polymers (South Bend, Ind., USA). If added, theoptional thickeners can be used in an amount up to 5 weight percentbased on the total weight of the latex composition (e.g., water andpolymeric latex particles). For example, the thickener can be used in anamount up to 4 weight percent, up to 3 weight percent, up to 2 weightpercent, or up to 1 weight percent. In some embodiments, the thickeneris in a range of 0 to 5 weight percent, 0.1 to 5 weight percent, 0.1 to2 weight percent, 0.1 to 1 weight percent, 0.2 to 0.8 weight percent, or0.4 to 0.6 weight percent.

The latex composition typically is dried to form a pressure-sensitiveadhesive. The compositions are typically dried to remove at least 90weight percent of the water. For example, at least 95 weight percent, atleast 97 weight percent, at least 98 weight percent, or at least 99weight percent of the water is removed. The water content of the driedpressure-sensitive adhesive many increase or decrease depending on theenvironmental humidity. In some embodiments, the latex composition iscoated on a substrate such as a backing layer or release liner prior todrying. Drying typically occurs at temperatures above room temperaturebut not at a temperature that would distort or degrade the substrateand/or the pressure-sensitive adhesive layer. In some embodiments, thedrying occurs at temperatures in a range of about 40° C. to about 120°C. and for a time sufficient to lower the water content to the desiredlevel.

The pressure-sensitive adhesive layer can have any desired thickness. Inmany embodiments, the adhesive layer has a thickness no greater than 20mils (500 micrometers), no greater than 10 mils (250 micrometers), nogreater than 5 mils (125 micrometers), no greater than 4 mils (100micrometers), no greater than 3 mils (75 micrometers), or no greaterthan 2 mils (50 micrometers). The thickness is often at least 0.5 mils(12.5 micrometers) or at least 1 mil (25 micrometers). For example, thethickness of the adhesive layer can be in the range of 0.5 mils (2.5micrometers) to 20 mils (500 micrometers), in the range of 0.5 mils (5micrometers) to 10 mils (250 micrometers), in the range of 0.5 mils(12.5 micrometers) to 5 mils (125 micrometers), in the range of 1 mil(25 micrometers) to 3 mils (75 micrometers), or in the range of 1 mil(25 micrometers) to 2 mils (50 micrometers).

The pressure-sensitive adhesives can have a good balance of peelstrength and adhesive strength. The presence of the second(meth)acrylate polymer in the droplets of the emulsion may contribute tothis good balance. Without the use of the second (meth)acrylate in theemulsion composition, it can be difficult to prepare pressure-sensitiveadhesives with this good balance. That is, the peel strength can beincreased while maintaining good cohesive strength. Likewise, thecohesive strength can be increased while maintaining good peel strength.

Various types of articles can be prepared that include a substrate and apressure-sensitive adhesive layer positioned adjacent to (and adheredto) a major surface of the substrate. Any suitable substrate can be usedin the article and the substrate is often selected depending on theparticular application. For example, the substrate can be flexible orinflexible and can be formed from a polymeric material, glass or ceramicmaterial, metal or metal alloy, or combination thereof. Some substratesare polymeric materials such as those prepared, for example, frompolyolefins (e.g., polyethylene, polypropylene, or copolymers thereof),polyurethanes, polyvinyl acetates, polyvinyl chlorides, polyesters(e.g., polyethylene terephthalate or polyethylene naphthalate),polycarbonates, polyacrylates such as polymethyl(meth)acrylates (PMMA),ethylene-vinyl acetate copolymers, neoprenes, and cellulosic materials(e.g., cellulose acetate, cellulose triacetate, and ethyl cellulose).The substrate can be in the form of foils, films, or sheets, nonwovenmaterials (e.g., paper, fabric, nonwoven scrims), foams, and the like.

For some substrates, it may be desirable to treat the surface of thesubstrate to improve adhesion to the pressure-sensitive adhesive layer.Such treatments include, for example, application of primer layers,surface modification layer (e.g., corona treatment or surface abrasion),or both. Illustrative examples of suitable chemical primer layer typesinclude urethanes, silicones, epoxy resins, vinyl acetate resins,ethyleneimines, and the like. Urethane and silicone types areparticularly effective chemical primers for use with polyester filmsubstrates. One suitable silicone type of primer layer has a continuousgelled network structure of inorganic particles, and is described inJapanese Unexamined Pat. Publication (Kokai) No. 2-200476. This primerlayer has a strong affinity for polyester resins and polyolefin resins.Illustrative examples of chemical primers for vinyl and polyethyleneterephthalate films include the crosslinked acrylic ester/acrylic acidcopolymers disclosed in U.S. Pat. No. 3,578,622 (Brown).

In some embodiments, the substrate is a release liner. Release linerstypically have low affinity for the pressure-sensitive adhesive layer.Exemplary release liners can be prepared from paper (e.g., Kraft paper)or other types of polymeric material. Some release liners are coatedwith an outer layer of a release agent such as a silicone-containingmaterial or a fluorocarbon-containing material.

Some articles are adhesive tapes. The adhesive tapes can be single-sidedadhesive tapes with the pressure-sensitive adhesive on a single side ofthe backing layer or can be double-sided adhesive tape with apressure-sensitive adhesive layer on both major surfaces of the backinglayer. The backing layer is often a polymeric film, fabric, or foam.Each pressure-sensitive adhesive layer may be positioned, if desired,between the backing layer and a release layer.

Any suitable backing layer can be used. In some embodiments, the backinglayer is an oriented polyolefin film. For example, the orientedpolyolefin film can prepared as described in U.S. Pat. No. 6,638,637(Hager et al.). Such backings layers often include multiple layers ofpolyolefins with at least two different melting points and that arebiaxially oriented. In another example, the oriented polyolefin film canbe prepared as described in U.S. Pat. No. 6,451,425 (Kozulla et al.).Such backings often include an isotactic polypropylene that is blendedor mixed with at least one second polyolefin such as polyethylene,polybutylene, or syndiotactic polypropylene. These backings aretypically biaxially oriented.

For adhesive tapes with a single pressure-sensitive adhesive layer, thebacking layer often has a first surface that has been treated (i.e.,primed) to improve adhesion to the pressure-sensitive adhesive layer.The backing layer has a second surface opposite the first surface thathas a low adhesion to the pressure-sensitive adhesive layer. Such anadhesive tape can be formed into a roll. In some embodiments, theadhesive tapes are packaging tapes.

Other articles are transfer tapes in which a pressure-sensitive adhesivelayer is positioned adjacent to a release liner. The transfer tape canbe used to transfer the pressure-sensitive adhesive layer to anothersubstrate or surface. Any suitable release liner can be used. In manyembodiments, the release liner has a release layer coating adjacent to asubstrate. Suitable substrates include, but are not limited to, papersuch as poly-coated Kraft paper and super-calendered or glassine Kraftpaper; cloth (fabric); nonwoven web; metal or metal alloy includingmetal foil; polyesters such as poly(alkylene terephthalate) such aspoly(ethylene terephthalate), poly(alkylene naphthalate) such aspoly(ethylene naphthalate); polycarbonate; polyolefins such aspolypropylene, polyethylene, polybutylene, and copolymers thereof;polyamide; cellulosic materials such as cellulose acetate or ethylcellulose; and combinations thereof.

In some exemplary embodiments, the release liners have a release coatingcontaining a polymerized product of a vinyl-silicone copolymers asdescribed in U.S. Pat. No. 5,032,460 (Kantner et al.). In otherexemplary embodiments, the release liner has a release coatingcontaining a polymerized product of a (meth)acrylate-functionalizedsiloxane as described in U.S. Patent Application Publication No.2013/059105 (Wright et al.). Such release coatings can be prepared byapplying a coating of a polymerizable composition containing the(meth)acrylate-functionalized polysiloxane to a surface of a substrateand then irradiating the coating with ultraviolet radiation. Theultraviolet radiation is often provided by short wavelengthpolychromatic ultraviolet light source having at least one peak withintensity at a wavelength in the range of about 160 to about 240nanometers. Suitable short wavelength polychromatic ultraviolet lightsources include, for example, low pressure mercury vapor lamps, lowpressure mercury amalgam lamps, pulsed Xenon lamps, and glow dischargefrom a polychromic plasma emission source. The coatings applied to thesubstrate can be free or substantially free (e.g., less than 0.1 weightpercent, less than 0.01 weight percent, or less than 0.001 weightpercent) of a photoinitiator based on the total weight of the coatings.

The pressure-sensitive adhesive layers often have both high peeladhesion (i.e., peel strength) and high shear strength (i.e., cohesion)to both smooth and rough surfaces. As such, the pressure-sensitiveadhesives can be used in articles having a diverse range of uses and canbe adhered to a variety of substrates. In some embodiments, thesubstrate is a polymeric film or sheet, metal or metal alloy, fabric, orfoam.

In embodiments where no tackifier or low amounts of tackifier are used,the pressure-sensitive adhesives are well suited for applications wherelow volatile organic content is needed such as for automotive interiorapplications. The pressure-sensitive adhesives often have both high peeladhesion and high shear strength (i.e., cohesion), particularly whenadhered to low surface energy substrates such as polyolefin (e.g.,polypropylene, polyethylene, polybutylene, and copolymers thereof) andclear coats. The good adhesive characteristics (e.g., high peel adhesionand high shear strength) can typically be maintained even attemperatures above room temperature such as those near 70° C.

In embodiments where a tackifier is included, the pressure-sensitiveadhesives often have both high peel adhesion and high shear strength,particularly when adhered to polar surfaces such as metals or metalalloys (e.g., carbon steel and stainless steel).

Embodiment 1 is an emulsion composition that contains a) water, b) apolymerizable surfactant having an unsaturated group that can undergofree radical polymerization, c) a first monomer composition, and d) asecond (meth)acrylate polymer. The first monomer composition includes analkyl (meth)acrylate having a linear or branched alkyl group with atleast six carbon atoms. The second (meth)acrylate polymer is present inan amount of 0.5 to 15 weight percent based on a total weight ofmonomers in the first monomer composition and has a glass transitiontemperature greater than or equal to 50° C. The second (meth)acrylatepolymer is formed from a second monomer composition containing at least50 weight percent of a cyclic alkyl (meth)acrylate based on a totalweight of monomers in the second monomer composition, wherein the cyclicalkyl group has at least six carbon atoms. The emulsion compositioncontains a first phase that includes the water and a second phasedispersed as droplets within the first phase. The droplets contain amixture of i) at least 90 weight percent of the first monomercomposition and ii) the second (meth)acrylate polymer. The second(meth)acrylate polymer is not miscible with the first phase and isdissolved in the first monomer composition within the droplets.

Embodiment 2 is the emulsion composition of embodiment 1, wherein thecyclic alkyl (meth)acrylate in the second monomer composition has aglass transition temperature equal to at least 80° C. when measured as ahomopolymer.

Embodiment 3 is the emulsion composition of embodiment 1 or 2, whereinthe first monomer composition further comprises a cyclic alkyl(meth)acrylate, polar monomer, or both.

Embodiment 4 is the emulsion composition of any one of embodiments 1 to3, wherein the first monomer composition comprises 60 to 98 weightpercent of the alkyl (meth)acrylate having a linear or branched alkylgroup with at least six carbon atoms, 1 to 30 weight percent of a cyclicalkyl (meth)acrylate, and 1 to 10 weight percent of the polar monomerbased on a total weight of monomers in the first monomer composition.

Embodiment 5 is the emulsion composition of any one of embodiments 1 to4, wherein the second monomer composition comprises 50 to 100 weightpercent of a cyclic alkyl (meth)acrylate and 0 to 50 weight percent ofan optional monomer that is a polar monomer, an alkyl (meth)acrylatehaving a linear or branched alkyl group, a vinyl monomer that does nothave a (meth)acryloyl group, (meth)acrylamide, (meth)acrylonitrile,N-alkyl (meth)acrylamide, N,N-dialkyl (meth)acrylamide, or a mixturethereof based on a total weight of monomers in the second monomercomposition.

Embodiment 6 is the emulsion composition of any one of claims 1 to 5,wherein the second monomer composition comprises 90 to 99 weight percentof the cyclic alkyl (meth)acrylate and 1 to 10 percent polar monomer or90 to 100 weight percent of the cyclic alkyl (meth)acrylate and 0 to 10weight percent polar monomer based on a total weight of monomers in thesecond monomer mixture.

Embodiment 7 is the emulsion composition of any one of embodiments 1 to6, wherein the first monomer composition is different than the secondmonomer composition.

Embodiment 8 is the emulsion composition of any one of embodiments 1 to7, wherein the second (meth)acrylate polymer has a weight averagemolecular weight in a range of 3,000 to 150,000 grams/mole.

Embodiment 9 is the emulsion composition of any one of embodiments 1 to8, wherein the emulsion composition does not contain a tackifier.

Embodiment 10 is the emulsion composition of any one of embodiments 1 to9, wherein the emulsion composition contains at least 25 weight percentwater based on a total weight of the emulsion composition.

Embodiment 11 is the emulsion composition of any one of embodiments 1 to10, wherein the emulsion composition contains up to 90 weight percentwater based on the total weight of the emulsion composition.

Embodiment 12 is the emulsion composition of any one of embodiments 1 to11, wherein the polymerizable surfactant is a propenyl polyoxyethylenealkylphenyl compound or propenyl polyoxyethylene alkylphenyl etherammonium sulfate compound.

Embodiment 13 is the emulsion composition of any one of embodiments 1 to12, wherein the polymerizable surfactant is sodium dodecylallylsulfosuccinate or a phosphate ester.

Embodiment 14 is the emulsion composition of any one of embodiments 1 to13, wherein the emulsion composition contains at least 0.5 weightpercent polymerizable surfactant based on the total weight of monomersin the first monomer composition.

Embodiment 15 is the emulsion composition of any one of embodiments 1 to14, wherein the emulsion composition contains up to 2 weight percentpolymerizable surfactant based on the total weight of monomers in thefirst monomers composition.

Embodiment 16 is a latex composition comprising a polymerized product ofthe emulsion composition of any one of embodiments 1 to 15, wherein thelatex composition comprises polymeric latex particles.

Embodiment 17 is the latex composition of embodiment 16, wherein thepolymeric latex particles have a single glass transition temperature asdetermined using a Differential Scanning Calorimeter.

Embodiment 18 is the latex composition of embodiment 16 or 17, whereinthe second (meth)acrylate polymer and a polymerized product of the firstmonomer composition are together in the same polymeric particles.

Embodiment 19 is the latex composition of any one of embodiments 16 to18, further comprising a tackifier that is water dispersible.

Embodiment 20 is the latex composition of any one of embodiments 16 to19, wherein the polymerized product of the emulsion compositioncomprises polymerized surfactant in an amount in a range of 1 to 2weight percent based on a total weight of the polymeric latex particles.

Embodiment 21 is a pressure-sensitive adhesive comprising a driedproduct of the latex composition of any one of embodiments 16 to 20.

Embodiment 22 is an article comprising (a) a substrate and (b) a firstpressure-sensitive adhesive layer positioned adjacent to a first majorsurface of the substrate, wherein the first pressure-sensitive adhesivelayer comprises the pressure-sensitive adhesive of embodiment 21.

Embodiment 23 is the article of embodiment 22, further comprising asecond layer of pressure-sensitive adhesive of embodiment 21 positionedadjacent to a second major surface of the substrate.

Embodiment 24 is the article of embodiment 22 or 23, wherein thesubstrate is a foam or polymeric film.

Embodiment 25 is the article of any one of embodiments 22 to 24, whereinthe substrate is a biaxially oriented polyolefin film.

Embodiment 26 is the article of any one of embodiments 22 to 24, whereinthe substrate is a release liner.

Embodiment 27 is the article of embodiment 26, wherein the release linercomprises a release coating comprising a polymerized product of avinyl-silicone copolymer or a (meth)acrylate-functionalized siloxane.

Embodiment 28 is the article of embodiment 26 or 27, wherein the articleis a transfer tape.

Embodiment 29 is the article of embodiment 22 to 25, wherein the articleis an adhesive tape.

Embodiment 30 is the article of embodiment 29, wherein the adhesive tapeis a packaging tape.

Embodiment 31 is the article of any one of embodiments 22 to 25, whereinthe substrate has a low energy surface.

Embodiment 32 is the article of embodiment 31, wherein the low energysurface comprises a polyolefin or a clear coat.

Embodiment 33 is a method of forming a pressure-sensitive adhesive. Themethod includes (a) forming an emulsion composition of any one ofembodiments 1 to 15, (b) polymerizing the emulsion composition to form alatex composition comprising polymeric latex particles, and (c) dryingthe latex composition to form the pressure-sensitive adhesive.

Embodiment 34 is the method of embodiment 33, wherein forming theemulsion composition comprises forming the second (meth)acrylatepolymer, dissolving the second (meth)acrylate polymer in one or moremonomers in the first monomer composition to form a polymer solution,adding the polymer solution to the first phase, and forming droplets ofthe polymer solution within the first phase by mixing with high shear.

EXAMPLES

All parts, percentages, ratios, etc. used in the Examples are by weightunless indicated otherwise.

As used herein, the term “pph” refers to parts per hundred.

TABLE 1 Materials Abbreviation Description Supplier EHA 2-Ethylhexylacrylate Dow Chemical (Midland, MI, USA) IBOA Isobornyl acrylate SanEsters (New York, NY, USA) IBOMA Isobornyl methacrylate Sigma Aldrich(St. Louis, MO, USA) IOA Isooctyl acrylate 3M Company (St. Paul, MN,USA) AA Acrylic acid (99%) Alfa Aesar (Ward Hill, MA, USA) MAAMethacrylic acid (99%) Alfa Aesar (Ward Hill, MA, USA) EtOAc Ethylacetate Sigma Aldrich (St. Louis, MO, USA) MEHQ Methoxyetherhydroquinone Sigma Aldrich (St. Louis, MO, USA) IOTG Isooctylthioglycolate Sigma Aldrich (St. Louis, MO, USA) IRGACURE2,2-Dimethoxy-1,2-diphenyl-ethanone BASF (Ludwigshafen, Germany) 651IRGANOX Pentaerythritol tetrakis (3-(3,5-di-tert- BASF (Ludwigshafen,Germany) 1010 butyl-4-hydroxyphenyl) propionate) LUPERSOL2,5-Dimethyl-2,5-di(t- Atofina (Philadelphia, PA, USA) 101butylperoxy)hexene LUPERSOL 2,5-Dimethyl-2,5-di(t- Atofina(Philadelphia, PA, USA) 130 butylperoxy)hexyne-3 VAZO 522,2′-Azobis(2,4-dimethylpentanenitrile) DuPont (Wilmington, DE, USA)VAZO 67 2,2′-Azobis(2-methylbutanenitrile) DuPont (Wilmington, DE, USA)VAZO 88 1,1′-Azobis(cyclohexanecarbonitrile) DuPont (Wilmington, DE,USA) KPS Potassium persulfate (99.9% purity) Alfa Aesar (Ward Hill, MA,USA) Na₂S₂O₅ Sodium bisulfate (97% purity) Alfa Aesar (Ward Hill, MA,USA) FeSO₄•7H₂O Ferrous sulfate heptahydrate Sigma Aldrich (St. Louis,MO, USA) DIANAL Described by vendor as a methyl Dianal America, Inc.(Pasadena, TX, BR113 methacrylate resin; the M_(w) was about USA) 30kg/mol DIANAL Described by vendor as a butyl Dianal America, Inc.(Pasadena, TX, MB2543 methacrylate resin with a molecular USA) weight ofabout 35 kg/mole TRITON X-100 Nonionic surfactant Dow Chemical (Midland,MI, USA) DS-4 Sodium dodecyl benzene sulfonate Rhodia Inc., which is amember of the surfactant Solvay Group (Cranbury, NJ, USA) DS-10 Sodiumdodecyl benzene sulfonate Rhodia Inc., which is a member of thesurfactant Solvay Group (Cranbury, NJ, USA) HITENOL Polyoxyethylenealkylphenyl propenyl Dai-Ichi Kogyo Seiyaku Co., Ltd. BC-1025 etherammonium sulfate (25 wt. % solids (Japan) solution in water), which is apolymerizable surfactant SNOWTACK Water-dispersed tackifier, polymericLawter Inc. (Chicago, IL, USA) SE780G material based on rosin adductionand esterification TEGO RC-902 Silicone acrylate with a high silicone toEvonik North America, Inc. acrylate ratio (Parsippany, NJ, USA) TEGOSilicone acrylate with a low silicone to Evonik North America, Inc.RC-711 acrylate ratio (Parsippany, NJ, USA) PARAGUM Polyacrylatethickener Royal Coatings & Specialty Polymers 500 (South Bend, IN, USA)Test Method 1: Polymer Molecular Weight Measurement

The molecular weight distribution of the compounds was characterizedusing gel permeation chromatography (GPC). The GPC instrumentation,which was obtained from Waters Corporation (Milford, Mass., USA),included a high pressure liquid chromatography pump (Model 1515HPLC), anauto-sampler (Model 717), a UV detector (Model 2487), and a refractiveindex detector (Model 2410). The chromatograph was equipped with two 5micrometer PLgel MIXED-D columns available from Varian Inc. (Palo Alto,Calif., USA).

Samples of polymeric solutions were prepared by dissolving dried polymersamples in tetrahydrofuran at a concentration of 0.5 percent(weight/volume) and filtering through a 0.2 micrometerpolytetrafluoroethylene filter that is available from VWR International(West Chester, Pa., USA). The resulting samples were injected into theGPC and eluted at a rate of 1 milliliter per minute through the columnsmaintained at 35° C. The system was calibrated with polystyrenestandards using a linear least squares analysis to establish a standardcalibration curve. The weight average molecular weight (M_(w)) and thepolydispersity index (weight average molecular weight divided by numberaverage molecular weight (M_(n))) were calculated for each sampleagainst this standard calibration curve.

Test Method 2: Viscosity

The viscosity was measured with a Brookfield viscometer with spindle 3(obtained from Brookfield Engineering (Middleboro, Mass., USA)) at arotating speed of 30 revolutions per minute (rpm).

Test Method 3: Latex Weight Percent (Wt. %) Solids

To measure solid content, first an aluminum dish was weighed, then about0.2 to 0.3 grams of latex was added in the dish. The latex was dilutedby adding about 0.5 grams distilled deionized water. The dish was heatedin an 80° C. oven for about 4 hours until the weight did not change anymore. The weight percent solids (wt. % solids) was calculated accordingto the following equation:Wt. % solids=100λ(W2−W1)/(W3−W1)In this equation, W2 is the weight of the dish plus the weight of thedried polymer latex, W1 is the weight of the dish, and W3 is the weightof the dish plus the weight of the wet polymer latex.Test Method 4: Latex pH

The latex pH was measured with a pH meter (from Chemtrix, Rolling HillsEstates, CA, USA under the trade designation “MODEL 60A pH METER”).

Test Method 5: Glass Transition of Polymer (T_(g)) by DifferentialScanning Calorimetry (DSC)

Polymer samples were dried to remove water and/or organic solvent. Thedried samples were then weighed and loaded into TA Instruments T_(zero)aluminum hermetic DSC sample pans. The samples were analyzed using a TAInstruments Q2000 MODULATED DIFFERENTIAL SCANNING CALORIMETER (“Q2000MDSC”, including RC-03761 sample cell), utilizing a heat-cool-heatmethod in temperature-modulated mode (−90° C. to 125° C. at 5° C./min.with a modulation amplitude of ±0.796° C. and a period of 60 seconds)under a nitrogen atmosphere. TA Instruments is located in New Castle,Del., USA.

In temperature modulated mode, the Q2000 MDSC gave three signals:cumulative (standard) heat flow, reversing (Rev) heat flow, andnonreversing (Nonrev) heat flow. The cumulative heat flow signal was thesum of the reversing and nonreversing heat flow signals. The reversingsignal was the heat capacity (Cp) component, which exhibited changes inheat capacity and included transitions such as the T_(g) (glasstransition). The nonreversing signal was the kinetic component andincluded kinetic transitions such as crystallization and chemicalreactions.

Following data collection, the thermal transitions were analyzed usingthe TA UNIVERSAL ANALYSIS program. If present, any glass transitions(T_(g)) or significant endothermic or exothermic peaks were evaluated.The glass transition temperatures were evaluated using the step changein the standard heat flow (HF) or reversing heat flow (Cp related/REVHF) curves. The onset, midpoint (half height), and end temperatures ofthe transition were noted as well as the change in heat capacityobserved at the glass transition were calculated. Any peak transitionswere evaluated using the heat flow (HF), reversing heat flow (Rev HF) ornon-reversing heat flow (Nonrev HF) curves. Peak area values and/or peakminimum/maximum temperatures were also determined. The peak integrationresults were normalized for sample weight and reported in J/g.

Test Method 6: Particle Size Via Dynamic Light Scattering

For a polymer dispersion (or latex) with average particle size smallerthan 1 micrometer, the average particle size of latex samples wasmeasured with dynamic light scattering instrument (ZETASIZER NANO ZS,available from Malvern Instruments Ltd. (Worcestershire, UK)) withdiluted latex sample (approximately one drop of latex in 5 mL of water),following the manufacturer's instructions, and using polystyrene beadcalibration standards.

Test Method 7: Particle Size Via Laser Diffraction

For a polymer dispersion (or latex) with average particle size largerthan 1 micrometer, the average particle size was measured by laserdiffraction with an HORIBA LA-950 LASER DIFFRACTION PARTICLE SIZEANALYZER (Horiba Instruments, Inc., Kyoto, Japan) with a diluted latexsample (approximately 1:5 weight ratio of polymer dispersion to 1% DS-10surfactant solution in deionized water), following the manufacturer'sinstructions.

Test Method 8: 90 Degree Peel Adhesion Test to Polypropylene Substrate

A sample of pressure-sensitive adhesive to be tested was coated with ahand-spread knife onto a 2.0 mil (0.002 inches, approximately 51micrometer) polyester film (HOSTAPHAN 3 SAB, primed PET film, availablefrom Mitsubishi Polyester Film Inc. (Greer, S.C., USA)), and dried in a70° C. oven for 15 minutes to give a dry PSA thickness in a range of 0.9to 1.2 mil (approximately 23 to 30 micrometers). The coated film wasconditioned at 23° C. and 50 percent relative humidity for about 24hours, and then cut into strips of tape that were 0.5 inch(approximately 1.3 cm) wide.

Polypropylene (PP) test panels (5 cm×12.5 cm panels obtained fromAeromat Plastics (Burnsville, Minn., USA) were prepared by wiping thepanels 8 to 10 times using hand pressure with a tissue wetted with theisopropyl alcohol. The procedure was repeated two more times with cleantissues wetted with isopropyl alcohol. The cleaned panels were airdried.

To do the PP peel adhesion test, first the 0.5 inch (1.25 cm) wide stripof tape was applied to the PP substrate with a 2 kilograms (4.5 pounds)roller. Then the peel test was performed at a removal angle of 90degrees according to the procedure described in the ASTM Internationalstandard D3330/D3330M-04 (reproved in 2010), Method F.

Peel adhesion was assessed with an IMASS SP-2000 slip/peel tester(available from IMASS, Inc., Accord, Mass., USA) at a peel rate of 305mm/minute (12 inches/minute). Peel adhesion values were reported as bothounces per inch (oz/in) and Newtons per decimeter (N/dm).

Test Method 9: 180 Degree Peel Adhesion Test to Stainless SteelSubstrate

A sample of pressure-sensitive adhesive to be tested was coated with ahand-spread knife onto a 2.0 mil (0.002 inches, approximately 51micrometer) polyester film (HOSTAPHAN 3 SAB, primed PET film, availablefrom Mitsubishi Polyester Film Inc. (Greer, S.C., USA)), and dried in a70° C. oven for 15 minutes to give a dry PSA thickness in a range of 0.9to 1.2 mil (approximately 23 to 30 micrometers). The coated film wasconditioned at 23° C. and 50 percent relative humidity for 24 hours, andthen cut into strips of tape that were 0.5 inch (approximately 1.3 cm)wide.

The 0.5 inch (approximately 1.3 cm) wide strips of tape were applied toa stainless steel (SS) plate with a 2 kg (4.5 pound) roller and thenpeel adhesion was assessed with an IMASS SP-2000 slip/peel tester(available from IMASS, Inc. (Accord, Mass., USA)) using a peel angle of180 degrees and speed of 12 inches (approximately 30 cm) per minute.Peel adhesion values were reported as both ounces per inch (oz/in) andNewtons per decimeter (N/dm).

Test Method 10: Static Shear Strength at 70° C.

A sample of pressure-sensitive adhesive to be tested was coated with ahand-spread knife onto a 2.0 mil (0.002 inches, approximately 51micrometer) polyester film (HOSTAPHAN 3 SAB, primed PET film, availablefrom Mitsubishi Polyester Film Inc. (Greer, S.C., USA)), and dried in a70° C. oven for 15 minutes to give a dry PSA thickness in a range of 0.9to 1.2 mil (approximately 23 to 30 micrometers). The coated film wasconditioned at 23° C. and 50 percent relative humidity for 24 hours, andthen cut into strips of tape 0.5 inch (approximately 1.3 cm) wide.

The static shear strength of an adhesive was determined according toASTM International standard, D3654/D3654M-06 (reapproved in2011)—Procedure A, using a 500 grams load inside an oven set at 70° C. Atest specimen was prepared by laminating a 0.5 in. x 1 in. (1.3 cm×2.5cm) piece of adhesive or tape on a polypropylene (PP) or stainless steel(SS) panel. The time to failure, i.e., time in minutes for the weight topull the adhesive away from panel was recorded. If no failure wasobserved after 10,000 minutes, the test was stopped and a value of10,000+ minutes was recorded.

Testing Method 11: Fabric Bonding Adhesion Test

The fabric, which was a sport nylon (obtained from Joann Fabrics as itemnumber 1997147, royal blue color) was cut into 1 inch (about 2.5 cm)wide and 6 inch (15.2 cm) long strips. The adhesive tape was cut into0.5 inch (1.3 cm) wide and 7-8 inches (18 to 20 cm) long strips. Thetape strip was laid on the fabric strip. This testing sample waslaminated together with a 2 kg (4.5 pound) roller, and then dwelled for1 hour before testing. The end of fabric was then placed in the bottomjaw of an Instron device and the end of tape in the top jaw. The Instronsettings were set as follows: crosshead speed of 12 inch/min (30.5cm/min), and average load was taken between 2 inch (5.1 cm) and 5 inch(12.7 cm), which part was the middle portion of the sample. Threereadings were recorded, averaged and reported as the peel adhesion.

Preparatory Example 1 (PE-1)

A polymer was made with two steps. In the first step of thepolymerization, the reactor (an agitated stainless steel reactor) wascharged with a mixture consisting of 88 kg of IBOA and 2.72 kg ofacrylic acid (AA), along with 90.8 grams of IRGANOX 1010, 381 grams ofIOTG, 18.2 grams of MEHQ, and 1.8 grams of VAZO 52. The reactor wassealed and purged of oxygen and then held at approximately 5 psig (34.5kPa) nitrogen pressure. The reaction mixture was heated to 60° C. (140°F.) and the reaction proceeded adiabatically and peaked at a temperatureof 127° C. (260° F.). When the reaction was complete, the mixture wascooled to below 50° C.

In the second step, to the reaction product of the first step was added10.9 grams of VAZO 52, 3.6 grams of VAZO 67, 5.4 grams of VAZO 88, 5.4grams of LUPERSOL 101, and 7.3 grams of LUPERSOL 130 (the initiatorcomponents were added as a solution dissolved in a small amount of ethylacetate). An additional 191 grams of IOTG was then added. The reactorwas sealed and purged with nitrogen and held at 5 psig (34.5 kPa)nitrogen pressure. The reaction mixture was heated to 60° C. (140° F.)and the reaction proceeded adiabatically. After the reaction reachedpeak temperature of 176° C. (350° F.), the mixture was heated at thistemperature for 2 hours. The resulting polymeric material is referred toas PE-1. To get PE-1 out of the reactor, the heating jacket was drainedand EHA is added over a period of 2 hours. The resulting polymersolution, which contained PE-1 dissolved in the added EHA, was thencooled to 93° C. (200° F.) and stirred overnight.

As used herein, the term “PE-1” refers to the polymeric material formedfrom IBOA/AA (97/3) and having a weight average molecular weight of 35kg/mole. All formulations below using PE-1 are based on the weight ofthe polymer rather than on the weight of the polymer solution formed bydissolving PE-1 in EHA. The EHA added to form the polymer solution isconsidered to be part of the first monomer composition.

Preparatory Example 2 (PE-2)

The polymerization was carried out by a two step reaction using a VSP2adiabatic reaction apparatus equipped with a 316 stainless steel testcan (available from Fauske and Associates Inc., Burr Ridge, Ill., USA).

In the first step of the polymerization, the test can in the VSP2reactor was charged with 80 grams of a monomer mixture (IBOA/AA: 97/3weight ratio). To the monomer mixture was added 0.1 pph of IRGANOX 1010,2 pph of chain transfer agent (IOTG), 0.02 pph of MEHQ, and 0.002 pph ofVAZO 52 with each pph based on the total weight of monomers in themonomer mixture. The reactor was sealed and purged with nitrogen andthen held at approximately 100 psig (689 kPa) nitrogen pressure. Thereaction mixture was heated to 60° C. and the reaction proceededadiabatically. The approximate peak temperature was about 180° C. Afterthe temperature peaked, the mixture was cooled to below 50° C.

In a second step, an initiator solution was added to 75 grams of thereaction product of the first step. The solution contained 0.012 pph ofVAZO 52, 0.004 pph of VAZO 67, 0.006 pph of VAZO 88, 0.006 pph ofLUPERSOL 101, and 0.008 pph of LUPERSOL 130 with each pph based on theweight of the polymeric material in the reaction product. The initiatorswere dissolved in a small amount of ethyl acetate and the totalinitiator solution weighed 0.7 grams. An additional amount of IOTG (1pph) was then added. The reactor was sealed, purged of oxygen, and heldat 100 psig (793 kPa) nitrogen pressure. The reaction mixture was heatedto 60° C. and the reaction proceeded adiabatically, with a peaktemperature of about 124° C. The reaction mixture was warmed to 170° C.and held at that temperature for 1 hour. The polymer was then cooled.The resulting polymer had a composition of IBOA/AA of 97/3 and M_(w) of8 kg/mol.

Preparatory Example 3 (PE-3)

The formulation and procedure was the same as PE-2 except the amount ofchain transfer agent and the reaction peak temperatures were altered. Instep 1, 1.1 pph of IOTG was added and the peak temperature was about134° C. In step 2, 0.55 pph of IOTG was added and the peak temperaturewas about 138° C. The resulting polymer had a composition of IOBA/AA of97/3 and M_(w) of 14 kg/mol.

Preparatory Example 4 (PE-4)

The formulation and procedure was the same as PE-2 except the amount ofchain transfer agent and the reaction peak temperatures were altered. Instep 1, 0.6 ppph of IOTG was added and the peak temperature was about130° C. In step 2, 0.3 pph of IOTG was added and the peak temperaturewas about 133° C. The resulting polymer had a composition of IOBA/AA of97/3 and M_(w) of 23 kg/mol.

Preparatory Example 5 (PE-5)

150 grams ethyl acetate, 37.50 grams IBOA, 11 grams IBOMA, 1.50 gramsAA, 0.25 grams VAZO 67, and 0.125 grams IOTG were charged into a bottle.Then the reactants were purged with nitrogen to remove the oxygen. Thebottle was then sealed and put in a launderometer to react at 60° C. for24 hours. Then the polymer solution was placed in an aluminum dish anddried in an oven to remove the solvent. The dried polymer had acomposition of IBOA/IBOMA/AA of 75/22/3 and M_(w) of about 34 kg/mol.

Preparatory Example 6 (PE-6)

A polymer was prepared by a bulk polymerization within a polymeric pouchinitiated by ultra-violet radiation according to the method described inPatent Application Publication No. WO 96/07522 and U.S. Pat. No.5,804,610 (Hamer et al.). The polymer was made with the formulation ofIOA (84.3 pph), IBOA (12.7 pph), AA (3 pph), IOTG (0.03 pph) andIRGACURE 651 (0.15 pph). Each pph was based on the total weight of allthe monomers. The polymer had composition of IOA/IBOA/AA (84.3/12.7/3)and Mw of about 625 kg/mol.

Preparatory Example 7 (PE-7)

A polymer was prepared by a bulk polymerization within a polymeric pouchinitiated by ultra-violet radiation according to the method described inPatent Application Publication No. WO 96/07522 and U.S. Pat. No.5,804,610 (Hamer et al.). The polymer was made with the formulation ofIOA (97 pph), AA (3 pph), IOTG (0.03 pph) and IRGACURE 651 (0.15 pph).Each pph was based on the total weight of all the monomers. The polymerhad composition of IOA/AA (97/3) and Mw of about 576 kg/mol.

Preparatory Example 8 (PE-8)

DS-10 (3.80 grams) along with 225 grams of deionized water were addedinto a beaker and stirred to form an aqueous solution. AA (9.5 grams),CBr₄ (0.18 grams), and IBOA (180.5 grams) were added to a separatebeaker and mixed well to form an oil phase. The aqueous and oil phaseswere then both poured into a 2-liter resin flask equipped with athermometer, mechanical agitator with glass retreat blade impeller,condenser, and nitrogen inlet tube. The reaction mixture was thenstirred at 300 revolutions per minute (rpm) under a blanket of nitrogen.The reactants were heated to 29° C., and then KPS (0.38 grams), Na₂S₂O₅(0.10 grams), and a solution of FeSO₄.7H₂O (0.0011 grams dissolved in0.5 grams H₂O) were added. The reaction resulted in an exotherm peaktemperature of 48° C. After the exotherm peak was reached, the reactantswere heated to 75° C. and maintained at that temperature for 1.5 hours.The latex was then cooled and filtered through cheese cloth to yield alatex having 39 weight percent solids, pH about 4.6, viscosity about2,000 centipoises, and average particle diameter of about 126nanometers. This latex polymer had a composition of IBOA/AA (97/3) andM_(w) of 162 kg/mol.

Preparatory Example 9 (PE-9)

First, an IBOA/AA (97/3) copolymer with M_(w) of about 34,000 g/mol wasprepared by a bulk polymerization within a polymeric pouch initiated byultra-violet radiation according to the method described in in PatentApplication Publication No. WO 96/07522 and U.S. Pat. No. 5,804,610(Hamer et al.). The polymer was made with the formulation of IBOA (97pph), AA (3 pph), IRGACURE 651 (1 pph), and IOTG (0.75 pph) where eachpph is based on the total weight of monomers.

Then 50 grams of the resulting polymer, 50 grams of toluene, 0.64 gramsTRITON X-100, 0.115 grams DS-4 were mixed together to form an oil phase.The aqueous phase was prepared by mixing together 25 grams water and0.115 grams DS-4. The aqueous phase solution and then the oil phasesolution were added to a 1 L stainless steel Waring blender. The mixturewas blended at the high speed setting for 2 minutes to give a polymeremulsion having about 40 weight percent solids, a viscosity of 3960centipoises, and an average particle diameter of about 2.9 micrometers.

TABLE 2 Summary of Preparatory Examples (PE-1 to PE-9) and DIANALPolymers Sample Composition M_(w) (kg/mol) T_(g) (° C.) PE-1 IBOA/AA(97/3) 35 95 PE-2 IOBA/AA (97/3) 8 74 PE-3 IBOA/AA (97/3) 14 85 PE-4IBOA/AA (97/3) 23 93 PE-5 IBOA/IBO/MA/AA 34 83 (75/22/3) PE-6IOA/IBOA/AA 625 −50 (84.3/12.7/3) PE-7 IOA/AA (97/3) 576 −52 PE-8IBOA/AA (97/3) 162 95 PE-9 IBOA/AA (97/3) 34 95 DIANAL Described byvendor as 35 60 BR113 a methyl methacrylate resin DIANAL Described byvendor as 30 88 MB2543 a butyl methacrylate resinThe T_(g) for PE-6 and PE-9 were calculated using the Fox Equation whilethe T_(g) for PE-1 to PE-5, DIANAL BR113, and DIANAL MB2543 weremeasured using modulated DSC.

Preparatory Example 10 (PE-10): Preparation of a Short-Wave UV-CuredLiner

A blend of 70 weight percent TEGO RC-902 and 30 weight percent TEGORC-711 was coated onto one side of a 50 micrometer thick unprimed PETfilm substrate (available from Mitsubishi Polyester Film, Inc. (Greer,S.C., USA)) to give a wet coating thickness of less than 1.0 micrometer.The coated film was then exposed to the output of three 150Wlow-pressure mercury amalgam lamps (manufactured by Heraeus Noblelight(Hanau, Germany)) with a peak intensity at 185 nm in a nitrogenatmosphere and at a web speed of 15.2 meters per minute (mpm) to providea short-wave UV-cured liner having a cured release surface. Otherinformation about this liner can be found in U.S. Patent ApplicationPublication No. 2013/0059105 (Wright et al.).

Example 1 (EX-1)

The aqueous phase was prepared by mixing 15.6 grams of HITENOL BC1025and 208 grams of de-ionized water in a beaker. The oil phase wasprepared by mixing 267 grams of 2-ethylhexyl acrylate (EHA), 40.5 gramsisobornyl acrylate (IBOA), 5.7 grams of acrylic acid (AA), 3.8 grams ofmethacrylic acid (MAA), and 9.5 grams of the polymer of PreparatoryExample 1 (PE-1) in a beaker until of solution was formed. For furtherclarification, PE-1 refers to the polymer formed from IBOA/AA (97/3).The amount of EHA included in the polymer solution containing dissolvedPE-1 (the amount of EHA added to remove PE-1 from the reactor in whichit was prepared) was included in the total amount of EHA added (267grams). The oil phase had a total weight of 326.5 grams. The oil phasewas then poured into the aqueous phase and mixed well. The content waspoured into a 1-liter stainless steel Waring blender container andhomogenized with the blender at the high speed setting for 2 minutes.The mixture was then poured into a 2-liter resin flask equipped with athermometer, mechanical agitator with glass retreat blade impeller,condenser, and nitrogen inlet tube. Then, 0.4 grams of potassiumpersulfate (KPS) was added. The reaction mixture was stirred under anitrogen blanket and heated to 60° C. and maintained at 60° C. for 4hours. The temperature was then increased to 80° C. within 30 min andmaintained at this temperature for 1 hour. The latex was then cooled andfiltered through cheesecloth to give the latex of EX-1. The latex wasEHA/IBOA/AA/MMA/PE-1 (84/13/2/1/3). The pH was about 2.8.

FIG. 1 shows the Modulated DSC heat flow signal from the second heating(2H) cycle for the latex polymer of EX-1 as a function of temperature ina nitrogen atmosphere.

Example 2 to Example 5 (EX-2 to EX-5)

These latexes were made the same way (mini-emulsion process) with thesame formulation as in EX-1, except PE-2 (for EX-2), PE-3 (for EX-3),PE-4 (for EX-4), and PE-5 (for EX-5) were used in place of PE-1.

FIG. 2 shows the Modulated DSC heat flow signal from the second heating(2H) cycle for the latex particle of EX-2 as a function of temperaturein a nitrogen atmosphere.

Comparative Examples 1 and 2 (CE-1 and CE-2)

These two latexes were made the same way (mini-emulsion process) withthe same formulation as in EX-1 except that either DIANAL BR113 (forCE-1) or DIANAL MB2543 (for CE-2) was used in place of PE-1. UnlikePE-1, neither DIANAL MB2543 nor DIANAL BR113 was prepared from a monomerhaving a ring structure. The solid content of CE-1 and CE-2 were bothabout 60 weight percent. The viscosities were 270 centipoises for CE-1and 220 centipoises for CE-2. The average particle diameters were about413 nm for CE-1 and 426 nm for CE-2.

Comparative Example 3 (CE-3)

This latex was made the same way (mini-emulsion process) with the sameformulation as in EX-1 except that Preparatory Example 6 (PE-6) was usedin place of PE-1. The resulting latex had a solid of 60 weight percent,a viscosity of 92 centipoises, and an average particle diameter of 548nm.

Comparative Example 4 (CE-4)

This latex was made the same way (mini-emulsion process) with the sameformulation as in EX-1 except for that Preparatory Example 7 (PE-7) wasused in place of PE-1. After polymerization, ammonia was added in thelatex to adjust the latex pH to about 4. The resulting latex had asolids content of 58 weight percent.

Comparative Example 5 (CE-5)

This latex according to the same method as EX-1, except that neitherPE-1 nor any other previously formed polymer was added. The reactantscoagulated during the polymerization reaction and no latex was obtained.

TABLE 3 Composition of EX-1 to EX-5 and CE-1 to CE-5 Average Solidsparticle Approximate content, Viscosity, diameter, T_(g), ExampleComposition wt. % cps nm ° C. EX-1 EHA/IBOA/AA/MMA/PE-1 62 390 392 −48(84/13/2/1/3) EX-2 EHA/IBOA/AA/MMA/PE-2 62 612 385 −47 (84/13/2/1/3)EX-3 EHA/IBOA/AA/MMA/PE-3 60 440 437 −47 (84/13/2/1/3) EX-4EHA/IBOA/AA/MMA/PE-4 63 936 447 −47 (84/13/2/1/3) EX-5EHA/IBOA/AA/MMA/PE-5 59 136 400 −47 (84/13/2/1/3) CE-1 EHA/IBOA/AA/MMA/60 270 413 −50 DIANAL MB2543 (84/13/2/1/3) CE-2 EHA/IBOA/AA/MMA/ 60 220420 −50 DIANAL BR113 (84/13/2/1/3) CE-3 EHA/IBOA/AA/MMA/PE-6 60 92 548−50 (84/13/2/1/3) CE-4 EHA/IBOA/AA/MMA/PE-7 58 110 508 −50 (84/13/2/1/3)CE-5 EHA/IBOA/AA/MMA N/A N/A N/A N/A (87/13/2/1)The T_(g) for CE-4 was calculated using the Fox Equation while the T_(g)of EX-1 to EX-5 and CE-1 to CE-3 were measured using modulated DSC. N/Ameans not analyzed because a latex did not form.

TABLE 4 Adhesive Properties of EX-1 to EX-5 and CE-1 to CE-4 70° C.Shear 70° C. Shear Peel - SS, Peel - PP, on SS, on PP, Example oz/in(N/dm) oz/in (N/dm) minutes minutes EX-1 53.4 (58.4) 24.5 (26.9) 1000010000 EX-2 48.8 (53.4) 25.5 (27.9) 10000 309 EX-3 52.9 (57.9) 25.5(27.9) 10000 369 EX-4 51.3 (56.2) 24.58 (26.9)  10000 394 EX-5 49.6(54.3) 16.7 (18.3) 10000 10000 CE-1 46.8 (51.3) 13.8 (15.1) 10000 171CE-2 44.6 (48.8) 16.6 (18.2) 10000 151 CE-3 44.6 (48.8) 16.1 (17.6)10000 159 CE-4 25.7 (28.2) 18.2 (20.0) 10,000 115

Comparative Example 6 (CE-6)

30 grams of CE-3 (60 weight percent solids) having a T_(g) of −50° C.was blended with 1.43 grams of PE-8 (39 wt. % solids) having a T_(g) of95° C. The weight ratio of the CE-3 polymer to the PE-8 polymer was 100to 3 (100:3). The adhesives properties of the blend were measured usingTest Methods 8, 9, and 10 and are shown in Table 5.

Comparative Example 7 (CE-7)

30 grams of CE-4 (58 weight percent solids) having a T_(g) of −50° C.was blended with 1.3 grams of PE-9 (40 wt. % solids) having a T_(g) of95° C. The weight ratio of the CE-4 polymer to the PE-9 polymer was 100to 3 (100:3). The adhesive properties of the blend were measured usingTest Methods 8, 9, and 10 and are shown in Table 5.

TABLE 5 Comparison of Adhesive Properties for CE-3, CE-4, CE-6, CE-7,and EX-1 70° C. 70° C. Peel - SS, Peel - PP, Shear Shear oz/in oz/in onSS, on PP, Sample Composition (N/dm) (N/dm) minutes minutes CE-3EHA/IBOA/AA/MMA/PE-6 (84/13/2/1/3) 44.6 16.1 10000 159 where PE-6 has aT_(g) of −50° C. (48.8) (17.6) CE-4 EHA/IBOA/AA/MMA/PE-7 (84/13/2/1/3)25.7 18.2 10000 115 where PE-7 has a T_(g) of −52° C. (28.2) (20.0) CE-6100:3 blend of CE-3 with a T_(g) of −50° C. and 45.2 12.0 10000 166 PE-8with a T_(g) of 95° C. (49.4) (13.2) CE-7 100:3 blend of CE-4 with aT_(g) of −50° C. and 20.6  8.1 N/A 147 PE-9 with a T_(g) of 95° C.(22.5)  (8.9) EX-1 EHA/IBOA/AA/MMA/PE-1 (84/13/2/1/3) 53.4 24.6 1000010000 where PE-1 has a T_(g) of 95° C. (58.4) (26.9)

Example 6 (EX-6)

A 30 gram sample of the polymeric latex of EX-1 (60% solid) was blendedwith 0.22 grams of PARAGUM 500 thickener. Ammonium was added into themixture to adjust the pH to about 9.

A sample of the polymeric latex blend of EX-6 was coated with ahand-spread knife coater onto the cured release surface of the releaseliner of Preparatory Example 10 (PE-10) and then dried in a 70° C. ovenfor 20 minutes to give a “transfer tape” having a latex PSA layer withdry thickness of about 2 mil (0.002 inches, about 51 micrometers).

Example 7 (EX-7)

A 30 gram sample of the polymeric latex of EX-1 (60% solid) was blendedwith 0.3 grams of PARAGUM 500 thickener and 6.1 grams of SNOWTACK SE780G(55% solid) tackifier. The ratio of EX-1 dry polymer to dry tackifierwas about 100:20. The pH of the resulting polymeric latex blend wasadjusted to about 9.

A sample of the polymeric latex blend of EX-7 was coated withhand-spread knife coater onto the cured release surface of the releaseliner of Preparatory Example 10 (PE-10) and then dried in a 70° C. ovenfor 20 minutes to give a “transfer tape” having a latex PSA layer withdry thickness of about 2 mil (about 51 micrometers).

Release and Re-Adhesion Testing Preparation of EX-6 and EX-7 “TransferTapes”

Samples of “transfer tape” from Examples 6 and 7 were aged and/orconditioned under one of the three following conditions:

-   -   Condition 1: 23° C. at 50% relative humidity for 24 hours.    -   Condition 2: 23° C. at 50% relative humidity (RH) for 24 hours,        followed by 32° C. at 90% RH for 48 hours, and then        equilibrating for 1 hour at 23° C. at 50% relative humidity.    -   Condition 3: 23° C. at 50% relative humidity for 24 hours,        followed by heating in a 70° C. oven (humidity not controlled)        for 48 hours, and then equilibrating for 1 hour at 23° C. at 50%        relative humidity.

After the conditioning steps, a 25 micrometer (1.0 mil) primed PET filmwas laminated to the conditioned latex PSA layer to form laminated testsamples. The primed PET film was prepared by application of a sol-gelprimer as described in Japanese Patent No. J02200476-A and as furtherdescribed in U.S. Pat. No. 5,204,219 (Van Ooij et al.), European PatentNo. 0301827 B 1 (Woo et al.), and European Patent No. 0372756 (Strobelet al).

The peel adhesion value was a measure of the force required to pull thePET-backed adhesive tape from the short-wave UV-cured liner at an angleof 180 degrees at a rate of 30.5 cm/min (12 inches/minute). The IMASSMODEL SP2000 PEEL TESTER (IMASS Corp. (Accord, Mass., USA)) was used torecord the peel adhesion value, summarized as “Release” value in Table6.

To determine the re-adhesion value, PET-backed tape samples were peeledfrom the short-wave UV-cured liner using the Release testing method(Test Method 11), and the resulting PET-backed tape was then applied tothe surface of a clean stainless steel panel. The PET-backed tape samplewas rolled down against the panel by means of two passes with a 2 kgrubber roller at 61 cm/min (24 inches/min). The re-adhesion value was ameasure of the force required to pull the PET-backed tape from the steelsurface at an angle of 180 degrees at a rate of 30.5 cm/min (12inches/minute). The IMASS MODEL SP2000 PEEL TESTER was used to recordthe peel force, summarized as “Re-adhesion” value in Table 6.

TABLE 6 Performance of transfer tape samples EX-6 and EX-7 Condition 1Condition 2 Condition 3 Re- Re- Re- “Transfer adhesion, adhesion,adhesion, Tape” Release, oz/in Release, oz/in Release, oz/in Sample g/in(g/cm) (N/dm) g/in (g/cm) (N/dm) g/in (g/cm) (N/dm) EX-6 11.3 (4.4) 31.4(34.4) 10.5 (4.1) 30.2 (33.1) 19.4 (7.6) 28.8 (31.5) EX-7 11.1 (4.4)35.1 (38.4) 10.2 (4.0) 32.7 (35.8) 16.4 (6.5) 35.1 (38.4)

Example 8 (EX-8)

The latex of Example 1 (EX-1) was coated with hand-spread knife coateron 1 mil (0.001 inches, 0.0025 cm) primed PET film, which was preparedby application of a sol-gel primer as described in Japanese Patent No.J02200476-A. The latex was dried in 70° C. oven for 20 minutes to givedry adhesive thickness of 2 mil (0.002 inches, 0.005 cm). After beingconditioned in a constant temperature and humidity (23° C. and 50percent relative humidity) room for 24 hours, the PSA was evaluatedusing the fabric adhesion test (Test Method 11), with the result shownin Table 7.

Example 9 (EX-9)

The latex of Example 2 (EX-2) was coated with hand-spread knife coateron 1 mil (0.001 inches, 0.0025 cm) primed PET film, which was preparedby application of a sol-gel primer as described in Japanese Patent No.J02200476-A. The latex was dried in 70° C. oven for 20 minutes to givedry adhesive thickness of 2 mil (0.002 inches, 0.005 cm). After beingconditioned in a constant temperature and humidity (23° C. and 50percent relative humidity) room for 24 hours, the PSA was evaluatedusing the fabric adhesion test (Test Method 11), with the result shownin Table 7.

TABLE 7 Performance of fabric bonding samples EX-8 and EX-9 “Fabricbonding” Fabric bonding peel Sample adhesion, oz/in (N/dm) EX-8 10.6(11.6) EX-9 10.9 (11.9)

We claim:
 1. An emulsion composition comprising: a) water; b) apolymerizable surfactant having an unsaturated group that can undergofree radical polymerization; c) a first monomer compositioncomprising 1) an alkyl (meth)acrylate having a linear or branched alkylgroup with at least six carbon atoms; and d) a second (meth)acrylatepolymer in an amount of 0.5 to 15 wt % based on a total weight ofmonomers in the first monomer composition, wherein the second(meth)acrylate polymer has a T_(g) greater than or equal to 50° C. andwherein the second (meth)acrylate polymer is formed from a secondmonomer composition comprising 1) at least 50 weight percent of a cyclicalkyl (meth)acrylate based on a total weight of monomers in the secondmonomer composition, wherein the cyclic alkyl group has at least sixcarbon atoms; wherein the emulsion has a first phase comprising thewater and a second phase dispersed as droplets within the first phase;and the droplets comprise a mixture comprising 1) the second(meth)acrylate polymer; and 2) at least 90 weight percent of the firstmonomer composition, wherein the second (meth)acrylate polymer is notmiscible with the first phase and is dissolved in the first monomercomposition within the droplets.
 2. The emulsion composition of claim 1,wherein the first monomer composition further comprises a cyclic alkyl(meth)acrylate, a polar monomer, or both.
 3. The emulsion composition ofclaim 1, wherein the first monomer composition comprises 60 to 98 weightpercent of the alkyl (meth)acrylate having a linear or branched alkylgroup with at least six carbon atoms, 1 to 30 weight percent of a cyclicalkyl (meth)acrylate, and 1 to 10 weight percent of the polar monomer.4. The emulsion composition of claim 1, wherein the second monomercomposition comprises 50 to 100 weight percent of a cyclic alkyl(meth)acrylate and 0 to 50 weight percent of an optional monomer that isa polar monomer, an alkyl (meth)acrylate having a linear or branchedalkyl group, and a vinyl monomer that does not have a (meth)acryloylgroup, (meth)acrylamide, (meth)acrylonitrile, an N-alkyl(meth)acrylamide, N,N-dialkyl (meth)acrylamide, or a mixture thereof. 5.The emulsion composition of claim 1, wherein the second monomercomposition comprises 90 to 100 weight percent of the cyclic alkyl(meth)acrylate and 0 to 10 percent polar monomer.
 6. The emulsioncomposition of claim 1, wherein the first monomer composition isdifferent than the second monomer composition.
 7. The emulsioncomposition of claim 1, wherein the second (meth)acrylate polymer has aweight average molecular weight in a range of 3,000 to 150,000grams/mole.
 8. The emulsion composition of claim 1, wherein the emulsiondoes not contain a tackifier.
 9. A latex composition comprising apolymerized product of the emulsion composition of claim 1, wherein thelatex composition comprises polymeric latex particles.
 10. The latexcomposition of claim 9, wherein the polymeric latex particles have asingle glass transition temperature as determined using a DifferentialScanning Calorimeter.
 11. The latex composition of claim 9, wherein thesecond (meth)acrylate polymer and a polymerized product of the firstmonomer composition are together in the same polymeric particles. 12.The latex composition of claim 9, further comprising a tackifier that iswater dispersible.
 13. A pressure-sensitive adhesive comprising a driedproduct of the latex composition of claim
 9. 14. An article comprising:a) a substrate; and b) a first pressure-sensitive adhesive layerpositioned adjacent to a first major surface of the substrate, whereinthe first pressure-sensitive adhesive layer comprises thepressure-sensitive adhesive of claim
 13. 15. A method of forming apressure-sensitive adhesive, the method comprising a) forming anemulsion composition of claim 1; b) polymerizing the emulsioncomposition to form a latex composition comprising polymeric latexparticles; and c) drying the latex composition to form thepressure-sensitive adhesive.